This has started 2 days ago, cannot really put my finger on the root cause, and flakiness dashboard is not working.  Stack trace for flakes:

WebglConformance_conformance_textures_video_tex_2d_rgba_rgba_unsigned_short_5_5_5_1 (gpu_tests.webgl_conformance_integration_test.WebGLConformanceIntegrationTest) ... [18882:1299:0711/195327:WARNING:webmediaplayer_impl.cc(335)] Using MultibufferDataSource
[18882:1299:0711/195328:WARNING:webmediaplayer_impl.cc(335)] Using MultibufferDataSource
[18882:35391:0711/195328:ERROR:ffmpeg_demuxer.cc(1595)] OnReadFrameDone result=-541478725 IsMaxMemoryUsageReached=0
[18882:1299:0711/195328:WARNING:webmediaplayer_impl.cc(335)] Using MultibufferDataSource
[18882:1299:0711/195328:WARNING:webmediaplayer_impl.cc(335)] Using MultibufferDataSource
[18882:1299:0711/195328:FATAL:resource_multibuffer_data_provider.cc(76)] Check failed: byte_pos() < url_data_->length() (32768 vs. 20584) http://127.0.0.1:62714/resources/red-green.theora.ogv
0   libbase.dylib                       0x000000011eedfade _ZN4base5debug10StackTraceC2Ev + 30
1   libbase.dylib                       0x000000011eedfb45 _ZN4base5debug10StackTraceC1Ev + 21
2   libbase.dylib                       0x000000011ef64100 _ZN7logging10LogMessageD2Ev + 80
3   libbase.dylib                       0x000000011ef61cb5 _ZN7logging10LogMessageD1Ev + 21
4   libmedia_blink.dylib                0x00000001384bb5c0 _ZN5media31ResourceMultiBufferDataProvider5StartEv + 608
5   libmedia_blink.dylib                0x00000001384c5c9c _ZN5media19ResourceMultiBuffer12CreateWriterERKi + 156
6   libmedia_blink.dylib                0x000000013848a8ef _ZN5media11MultiBuffer9AddReaderERKiPNS0_6ReaderE + 1887
7   libmedia_blink.dylib                0x00000001384b6d01 _ZN5media17MultiBufferReader19UpdateInternalStateEv + 1361
8   libmedia_blink.dylib                0x00000001384b8083 _ZN5media17MultiBufferReader10SetPreloadExx + 307
9   libmedia_blink.dylib                0x00000001384aefc7 _ZN5media21MultibufferDataSource17UpdateBufferSizesEv + 1687
10  libmedia_blink.dylib                0x00000001384ae525 _ZN5media21MultibufferDataSource20CreateResourceLoaderExx + 773
11  libmedia_blink.dylib                0x00000001384af2d4 _ZN5media21MultibufferDataSource10InitializeERKN4base8CallbackIFvbELNS1_8internal8CopyModeE1EEE + 740
12  libmedia_blink.dylib                0x00000001384fb5d9 _ZN5media18WebMediaPlayerImpl6DoLoadEN5blink14WebMediaPlayer8LoadTypeERKNS1_6WebURLENS2_8CORSModeE + 2873
13  libmedia_blink.dylib                0x000000013850d80a _ZN4base8internal13FunctorTraitsIMN5media18WebMediaPlayerImplEFvN5blink14WebMediaPlayer8LoadTypeERKNS4_6WebURLENS5_8CORSModeEEvE6InvokeINS_7WeakPtrIS3_EEJRKS6_S9_RKSA_EEEvSC_OT_DpOT0_ + 186
14  libmedia_blink.dylib                0x000000013850d629 _ZN4base8internal12InvokeHelperILb1EvE8MakeItSoIRKMN5media18WebMediaPlayerImplEFvN5blink14WebMediaPlayer8LoadTypeERKNS6_6WebURLENS7_8CORSModeEENS_7WeakPtrIS5_EEJRKS8_SB_RKSC_EEEvOT_T0_DpOT1_ + 153
15  libmedia_blink.dylib                0x000000013850d561 _ZN4base8internal7InvokerINS0_9BindStateIMN5media18WebMediaPlayerImplEFvN5blink14WebMediaPlayer8LoadTypeERKNS5_6WebURLENS6_8CORSModeEEJNS_7WeakPtrIS4_EES7_S8_SB_EEEFvvEE7RunImplIRKSD_RKNSt3__15tupleIJSF_S7_S8_SB_EEEJLm0ELm1ELm2ELm3EEEEvOT_OT0_NS_13IndexSequenceIJXspT1_EEEE + 193
16  libmedia_blink.dylib                0x000000013850ce4c _ZN4base8internal7InvokerINS0_9BindStateIMN5media18WebMediaPlayerImplEFvN5blink14WebMediaPlayer8LoadTypeERKNS5_6WebURLENS6_8CORSModeEEJNS_7WeakPtrIS4_EES7_S8_SB_EEEFvvEE3RunEPNS0_13BindStateBaseE + 44
17  libchrome_dll.dylib                 0x000000010d45215e _ZNK4base8CallbackIFvvELNS_8internal8CopyModeE1EE3RunEv + 46
18  libchrome_dll.dylib                 0x0000000114071b73 _ZN27ChromeContentRendererClient14DeferMediaLoadEPN7content11RenderFrameEbRKN4base8CallbackIFvvELNS3_8internal8CopyModeE1EEE + 163
19  libcontent.dylib                    0x00000001286a6a6f _ZN4base8internal13FunctorTraitsIMN7content21ContentRendererClientEFvPNS2_11RenderFrameEbRKNS_8CallbackIFvvELNS0_8CopyModeE1EEEEvE6InvokeIPS3_JRKS5_RKbSB_EEEvSD_OT_DpOT0_ + 191
20  libcontent.dylib                    0x00000001286a68e9 _ZN4base8internal12InvokeHelperILb0EvE8MakeItSoIRKMN7content21ContentRendererClientEFvPNS4_11RenderFrameEbRKNS_8CallbackIFvvELNS0_8CopyModeE1EEEEJPS5_RKS7_RKbSD_EEEvOT_DpOT0_ + 121
21  libcontent.dylib                    0x00000001286a6848 _ZN4base8internal7InvokerINS0_9BindStateIMN7content21ContentRendererClientEFvPNS3_11RenderFrameEbRKNS_8CallbackIFvvELNS0_8CopyModeE1EEEEJNS0_17UnretainedWrapperIS4_EES6_bEEEFvSC_EE7RunImplIRKSE_RKNSt3__15tupleIJSG_S6_bEEEJLm0ELm1ELm2EEEEvOT_OT0_NS_13IndexSequenceIJXspT1_EEEESC_ + 168
22  libcontent.dylib                    0x00000001286a6364 _ZN4base8internal7InvokerINS0_9BindStateIMN7content21ContentRendererClientEFvPNS3_11RenderFrameEbRKNS_8CallbackIFvvELNS0_8CopyModeE1EEEEJNS0_17UnretainedWrapperIS4_EES6_bEEEFvSC_EE3RunEPNS0_13BindStateBaseESC_ + 68
23  libmedia_blink.dylib                0x00000001384fa9e1 _ZNK4base8CallbackIFvRKNS0_IFvvELNS_8internal8CopyModeE1EEEELS3_1EE3RunES6_ + 65
24  libmedia_blink.dylib                0x00000001384fa8ff _ZN5media18WebMediaPlayerImpl4loadEN5blink14WebMediaPlayer8LoadTypeERKNS1_20WebMediaPlayerSourceENS2_8CORSModeE + 799
25  libblink_core.dylib                 0x000000013975c84f _ZN5blink16HTMLMediaElement15startPlayerLoadERKNS_4KURLE + 2591
26  libblink_core.dylib                 0x0000000139759d18 _ZN5blink16HTMLMediaElement12loadResourceERKNS_20WebMediaPlayerSourceERKNS_11ContentTypeE + 2632
27  libblink_core.dylib                 0x000000013975924b _ZN5blink16HTMLMediaElement23loadSourceFromAttributeEv + 555
28  libblink_core.dylib                 0x0000000139758bab _ZN5blink16HTMLMediaElement19selectMediaResourceEv + 1147
29  libblink_core.dylib                 0x0000000139757115 _ZN5blink16HTMLMediaElement12loadInternalEv + 277
30  libblink_core.dylib                 0x0000000139752cc1 _ZN5blink16HTMLMediaElement14loadTimerFiredEPNS_5TimerIS0_EE + 113
31  libblink_core.dylib                 0x0000000139777153 _ZN5blink5TimerINS_16HTMLMediaElementEE5firedEv + 115
32  libblink_platform.dylib             0x0000000134732ccd _ZN5blink9TimerBase11runInternalEv + 781
33  libblink_platform.dylib             0x0000000134733068 _ZN5blink9TimerBase20CancellableTimerTask3runEv + 56
34  libscheduler.dylib                  0x00000001378268e9 _ZN9scheduler17WebTaskRunnerImpl7runTaskENSt3__110unique_ptrIN5blink13WebTaskRunner4TaskENS1_14default_deleteIS5_EEEE + 41
35  libscheduler.dylib                  0x0000000137827b5a _ZN4base8internal13FunctorTraitsIPFvNSt3__110unique_ptrIN5blink13WebTaskRunner4TaskENS2_14default_deleteIS6_EEEEEvE6InvokeIJS9_EEEvSB_DpOT_ + 362
36  libscheduler.dylib                  0x0000000137827990 _ZN4base8internal12InvokeHelperILb0EvE8MakeItSoIRKPFvNSt3__110unique_ptrIN5blink13WebTaskRunner4TaskENS4_14default_deleteIS8_EEEEEJSB_EEEvOT_DpOT0_ + 48
37  libscheduler.dylib                  0x0000000137827886 _ZN4base8internal7InvokerINS0_9BindStateIPFvNSt3__110unique_ptrIN5blink13WebTaskRunner4TaskENS3_14default_deleteIS7_EEEEEJNS0_13PassedWrapperISA_EEEEEFvvEE7RunImplIRKSC_RKNS3_5tupleIJSE_EEEJLm0EEEEvOT_OT0_NS_13IndexSequenceIJXspT1_EEEE + 118
38  libscheduler.dylib                  0x00000001378272ac _ZN4base8internal7InvokerINS0_9BindStateIPFvNSt3__110unique_ptrIN5blink13WebTaskRunner4TaskENS3_14default_deleteIS7_EEEEEJNS0_13PassedWrapperISA_EEEEEFvvEE3RunEPNS0_13BindStateBaseE + 44
39  libbase.dylib                       0x000000011eeb4a7e _ZNK4base8CallbackIFvvELNS_8internal8CopyModeE1EE3RunEv + 46
40  libbase.dylib                       0x000000011eee126e _ZN4base5debug13TaskAnnotator7RunTaskEPKcRKNS_11PendingTaskE + 654
41  libscheduler.dylib                  0x00000001377f58d5 _ZN9scheduler16TaskQueueManager24ProcessTaskFromWorkQueueEPNS_8internal9WorkQueueEPNS1_13TaskQueueImpl4TaskE + 1589
42  libscheduler.dylib                  0x00000001377f2133 _ZN9scheduler16TaskQueueManager6DoWorkEN4base9TimeTicksEb + 1187
43  libscheduler.dylib                  0x00000001377fa497 _ZN4base8internal13FunctorTraitsIMN9scheduler16TaskQueueManagerEFvNS_9TimeTicksEbEvE6InvokeINS_7WeakPtrIS3_EEJRKS4_RKbEEEvS6_OT_DpOT0_ + 199
44  libscheduler.dylib                  0x00000001377fa27f _ZN4base8internal12InvokeHelperILb1EvE8MakeItSoIRKMN9scheduler16TaskQueueManagerEFvNS_9TimeTicksEbENS_7WeakPtrIS5_EEJRKS6_RKbEEEvOT_T0_DpOT1_ + 127
45  libscheduler.dylib                  0x00000001377fa1d0 _ZN4base8internal7InvokerINS0_9BindStateIMN9scheduler16TaskQueueManagerEFvNS_9TimeTicksEbEJNS_7WeakPtrIS4_EES5_bEEEFvvEE7RunImplIRKS7_RKNSt3__15tupleIJS9_S5_bEEEJLm0ELm1ELm2EEEEvOT_OT0_NS_13IndexSequenceIJXspT1_EEEE + 160
46  libscheduler.dylib                  0x00000001377f9bbc _ZN4base8internal7InvokerINS0_9BindStateIMN9scheduler16TaskQueueManagerEFvNS_9TimeTicksEbEJNS_7WeakPtrIS4_EES5_bEEEFvvEE3RunEPNS0_13BindStateBaseE + 44
47  libbase.dylib                       0x000000011eeb4a7e _ZNK4base8CallbackIFvvELNS_8internal8CopyModeE1EE3RunEv + 46
48  libbase.dylib                       0x000000011eee126e _ZN4base5debug13TaskAnnotator7RunTaskEPKcRKNS_11PendingTaskE + 654
49  libbase.dylib                       0x000000011efa8c5d _ZN4base11MessageLoop7RunTaskERKNS_11PendingTaskE + 877
50  libbase.dylib                       0x000000011efa9244 _ZN4base11MessageLoop21DeferOrRunPendingTaskENS_11PendingTaskE + 68
51  libbase.dylib                       0x000000011efa9cbd _ZN4base11MessageLoop6DoWorkEv + 669
52  libbase.dylib                       0x000000011efbb4c8 _ZN4base24MessagePumpCFRunLoopBase7RunWorkEv + 104
53  libbase.dylib                       0x000000011efbb44c ___ZN4base24MessagePumpCFRunLoopBase13RunWorkSourceEPv_block_invoke + 28
54  libbase.dylib                       0x000000011ef6717a _ZN4base3mac15CallWithEHFrameEU13block_pointerFvvE + 10
55  libbase.dylib                       0x000000011efba9c5 _ZN4base24MessagePumpCFRunLoopBase13RunWorkSourceEPv + 101
56  CoreFoundation                      0x00007fff9483ea01 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
57  CoreFoundation                      0x00007fff94830b8d __CFRunLoopDoSources0 + 269
58  CoreFoundation                      0x00007fff948301bf __CFRunLoopRun + 927
59  CoreFoundation                      0x00007fff9482fbd8 CFRunLoopRunSpecific + 296
60  Foundation                          0x00007fff9065cb29 -[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 278
61  libbase.dylib                       0x000000011efbbfa9 _ZN4base20MessagePumpNSRunLoop5DoRunEPNS_11MessagePump8DelegateE + 137

Another WebGL conformance test seems to be failing:
WebglConformance_conformance_more_conformance_quickCheckAPI_B1
https://build.chromium.org/p/chromium.gpu/builders/Mac%2010.10%20Retina%20Release%20%28AMD%29/builds/11760/steps/webgl_conformance_tests%20on%20ATI%20GPU%20on%20Mac%20Retina%20on%20Mac-10.10/logs/stdio

WebglConformance_conformance_more_conformance_quickCheckAPI_D_G (gpu_tests.webgl_conformance_integration_test.WebGLConformanceIntegrationTest) ... [11464:1299:0713/094354:INFO:CONSOLE(67)]
"WebGL: INVALID_OPERATION: depthRange: zNear > zFar", source: http://127.0.0.1:52941/conformance/more/conformance/quickCheckAPI-D_G.html (67)
[11464:1299:0713/094354:INFO:CONSOLE(67)] "WebGL: INVALID_OPERATION: depthRange: zNear > zFar", source: http://127.0.0.1:52941/conformance/more/conformance/quickCheckAPI-D_G.html
(67)
[11464:1299:0713/094354:INFO:CONSOLE(67)] "WebGL: INVALID_OPERATION: depthRange: zNear > zFar", source: http://127.0.0.1:52941/conformance/more/conformance/quickCheckAPI-D_G.html
(67)
[11464:1299:0713/094354:INFO:CONSOLE(67)] "WebGL: INVALID_OPERATION: depthRange: zNear > zFar", source: http://127.0.0.1:52941/conformance/more/conformance/quickCheckAPI-D_G.html
(67)
[11464:1299:0713/094354:INFO:CONSOLE(67)] "WebGL: INVALID_OPERATION: depthRange: zNear > zFar", source: http://127.0.0.1:52941/conformance/more/conformance/quickCheckAPI-D_G.html
(67)
[11464:1299:0713/094354:INFO:CONSOLE(67)] "WebGL: INVALID_OPERATION: depthRange: zNear > zFar", source: http://127.0.0.1:52941/conformance/more/conformance/quickCheckAPI-D_G.html
(67)
[11464:1299:0713/094354:INFO:CONSOLE(67)] "WebGL: INVALID_OPERATION: depthRange: zNear > zFar", source: http://127.0.0.1:52941/conformance/more/conformance/quickCheckAPI-D_G.html
(67)
[11464:1299:0713/094354:INFO:CONSOLE(67)] "WebGL: INVALID_OPERATION: depthRange: zNear > zFar", source: http://127.0.0.1:52941/conformance/more/conformance/quickCheckAPI-D_G.html
(67)
[11464:1299:0713/094354:INFO:CONSOLE(67)] "WebGL: INVALID_OPERATION: depthRange: zNear > zFar", source: http://127.0.0.1:52941/conformance/more/conformance/quickCheckAPI-D_G.html

This second seems like a separate issue that I'll file separately.  The first is a duplicate.