Sample logs:

[ RUN      ] WebViewTests/WebViewTest.Shim_TestNestedSubframes/0
[54587:52251:1216/030458.445276:WARNING:mac_util.mm(222)] Failed to set backup exclusion for file '/private/var/folders/9x/6c6sv3cj4j53wzpzthbp4ksm0000gm/T/.org.chromium.Chromium.npMIeN/d7hZwu3/Default/History': Error Domain=NSOSStatusErrorDomain Code=-50 "The operation couldn’t be completed. (OSStatus error -50.)" (paramErr: error in user parameter list) (-50)
[54587:52251:1216/030458.467951:WARNING:mac_util.mm(222)] Failed to set backup exclusion for file '/private/var/folders/9x/6c6sv3cj4j53wzpzthbp4ksm0000gm/T/.org.chromium.Chromium.npMIeN/d7hZwu3/Default/Favicons': Error Domain=NSOSStatusErrorDomain Code=-50 "The operation couldn’t be completed. (OSStatus error -50.)" (paramErr: error in user parameter list) (-50)
[54592:771:1216/030458.664222:WARNING:vt_video_decode_accelerator_mac.cc(169)] Failed to create VTDecompressionSession: Error Domain=NSOSStatusErrorDomain Code=-8973 "The operation couldn’t be completed. (OSStatus error -8973.)" (codecOpenErr) (-8973)
[54592:771:1216/030458.665514:WARNING:vt_video_decode_accelerator_mac.cc(191)] Failed to create hardware VideoToolbox session
[54592:771:1216/030458.728256:ERROR:vt_video_encode_accelerator_mac.cc(518)]  VTCompressionSessionCreate failed: -12908
BrowserTestBase received signal: Terminated: 15. Backtrace:
0   libbase.dylib                       0x0000000127e8954e _ZN4base5debug10StackTraceC2Ev + 30
1   libbase.dylib                       0x0000000127e89615 _ZN4base5debug10StackTraceC1Ev + 21
2   browser_tests                       0x0000000113ffd97f _ZN7content12_GLOBAL__N_1L27DumpStackTraceSignalHandlerEi + 1471
3   libsystem_platform.dylib            0x00007fff8b5195aa _sigtramp + 26
4   ???                                 0x00000006fdce493e 0x0 + 30027958590
5   CoreFoundation                      0x00007fff8f808f15 __CFRunLoopServiceMachPort + 181
6   CoreFoundation                      0x00007fff8f808539 __CFRunLoopRun + 1161
7   CoreFoundation                      0x00007fff8f807e75 CFRunLoopRunSpecific + 309
8   HIToolbox                           0x00007fff87cdaa0d RunCurrentEventLoopInMode + 226
9   HIToolbox                           0x00007fff87cda7b7 ReceiveNextEventCommon + 479
10  HIToolbox                           0x00007fff87cda5bc _BlockUntilNextEventMatchingListInModeWithFilter + 65
11  AppKit                              0x00007fff8b80924e _DPSNextEvent + 1434
12  AppKit                              0x00007fff8b80889b -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 122
13  browser_tests                       0x00000001120da69a __71-[BrowserCrApplication nextEventMatchingMask:untilDate:inMode:dequeue:]_block_invoke + 106
14  libbase.dylib                       0x0000000127f259ba _ZN4base3mac15CallWithEHFrameEU13block_pointerFvvE + 10
15  browser_tests                       0x00000001120da538 -[BrowserCrApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 248
16  AppKit                              0x00007fff8b7fc99c -[NSApplication run] + 553
17  libbase.dylib                       0x0000000127f8b972 _ZN4base24MessagePumpNSApplication5DoRunEPNS_11MessagePump8DelegateE + 306
18  libbase.dylib                       0x0000000127f8a96a _ZN4base24MessagePumpCFRunLoopBase3RunEPNS_11MessagePump8DelegateE + 122
19  libbase.dylib                       0x0000000127f778b5 _ZN4base11MessageLoop10RunHandlerEv + 645
20  libbase.dylib                       0x000000012805aa23 _ZN4base7RunLoop3RunEv + 307
21  browser_tests                       0x0000000114107f04 _ZN7content14RunThisRunLoopEPN4base7RunLoopE + 52
22  browser_tests                       0x0000000114107e91 _ZN7content14RunMessageLoopEv + 49
23  browser_tests                       0x000000011a1537e9 _ZN28ExtensionTestMessageListener18WaitUntilSatisfiedEv + 73
24  browser_tests                       0x000000010d86af28 _ZN15WebViewTestBase10TestHelperERKNSt3__112basic_stringIcNS0_11char_traitsIcEENS0_9allocatorIcEEEES8_NS_10TestServerE + 7528
25  browser_tests                       0x000000010d89699c _ZN41WebViewTest_Shim_TestNestedSubframes_Test19RunTestOnMainThreadEv + 2204
26  browser_tests                       0x0000000111ec1ee6 _ZN20InProcessBrowserTest23RunTestOnMainThreadLoopEv + 1478
27  browser_tests                       0x0000000113ffd154 _ZN7content15BrowserTestBase28ProxyRunTestOnMainThreadLoopEv + 388
28  browser_tests                       0x0000000113fff4b5 _ZN4base8internal13FunctorTraitsIMN7content15BrowserTestBaseEFvvEvE6InvokeIPS3_JEEEvS5_OT_DpOT0_ + 133
29  browser_tests                       0x0000000113fff3d4 _ZN4base8internal12InvokeHelperILb0EvE8MakeItSoIRKMN7content15BrowserTestBaseEFvvEJPS5_EEEvOT_DpOT0_ + 68
30  browser_tests                       0x0000000113fff36b _ZN4base8internal7InvokerINS0_9BindStateIMN7content15BrowserTestBaseEFvvEJNS0_17UnretainedWrapperIS4_EEEEEFvvEE7RunImplIRKS6_RKNSt3__15tupleIJS8_EEEJLm0EEEEvOT_OT0_NS_13IndexSequenceIJXspT1_EEEE + 91
31  browser_tests                       0x0000000113fff2ac _ZN4base8internal7InvokerINS0_9BindStateIMN7content15BrowserTestBaseEFvvEJNS0_17UnretainedWrapperIS4_EEEEEFvvEE3RunEPNS0_13BindStateBaseE + 44
32  browser_tests                       0x000000010d79391b _ZNK4base8internal8RunMixinINS_8CallbackIFvvELNS0_8CopyModeE1ELNS0_10RepeatModeE1EEEE3RunEv + 59
33  browser_tests                       0x00000001120ea2dc _ZN22ChromeBrowserMainParts25PreMainMessageLoopRunImplEv + 12252
34  browser_tests                       0x00000001120e724d _ZN22ChromeBrowserMainParts21PreMainMessageLoopRunEv + 253
35  libcontent.dylib                    0x0000000131720821 _ZN7content15BrowserMainLoop21PreMainMessageLoopRunEv + 337
36  libcontent.dylib                    0x000000013172c875 _ZN4base8internal13FunctorTraitsIMN7content15BrowserMainLoopEFivEvE6InvokeIPS3_JEEEiS5_OT_DpOT0_ + 133
37  libcontent.dylib                    0x000000013172c794 _ZN4base8internal12InvokeHelperILb0EiE8MakeItSoIRKMN7content15BrowserMainLoopEFivEJPS5_EEEiOT_DpOT0_ + 68
38  libcontent.dylib                    0x000000013172c71b _ZN4base8internal7InvokerINS0_9BindStateIMN7content15BrowserMainLoopEFivEJNS0_17UnretainedWrapperIS4_EEEEEFivEE7RunImplIRKS6_RKNSt3__15tupleIJS8_EEEJLm0EEEEiOT_OT0_NS_13IndexSequenceIJXspT1_EEEE + 91
39  libcontent.dylib                    0x000000013172c62c _ZN4base8internal7InvokerINS0_9BindStateIMN7content15BrowserMainLoopEFivEJNS0_17UnretainedWrapperIS4_EEEEEFivEE3RunEPNS0_13BindStateBaseE + 44
40  libcontent.dylib                    0x000000013213804b _ZNK4base8internal8RunMixinINS_8CallbackIFivELNS0_8CopyModeE1ELNS0_10RepeatModeE1EEEE3RunEv + 59
41  libcontent.dylib                    0x000000013281bb03 _ZN7content17StartupTaskRunner14RunAllTasksNowEv + 531
42  libcontent.dylib                    0x000000013171cd39 _ZN7content15BrowserMainLoop18CreateStartupTasksEv + 1785
43  libcontent.dylib                    0x0000000131731f13 _ZN7content21BrowserMainRunnerImpl10InitializeERKNS_18MainFunctionParamsE + 2947
44  libcontent.dylib                    0x00000001317146ef _ZN7content11BrowserMainERKNS_18MainFunctionParamsE + 335
45  libcontent.dylib                    0x00000001339157b7 _ZN7content23RunNamedProcessTypeMainERKNSt3__112basic_stringIcNS0_11char_traitsIcEENS0_9allocatorIcEEEERKNS_18MainFunctionParamsEPNS_19ContentMainDelegateE + 599
46  libcontent.dylib                    0x00000001339176a6 _ZN7content21ContentMainRunnerImpl3RunEv + 1462
47  libcontent.dylib                    0x000000013391501d _ZN7content11ContentMainERKNS_17ContentMainParamsE + 349
48  browser_tests                       0x0000000113ffce13 _ZN7content15BrowserTestBase5SetUpEv + 13251
49  browser_tests                       0x0000000111ebeb5a _ZN20InProcessBrowserTest5SetUpEv + 3130
50  browser_tests                       0x000000010fea7f6e _ZN20ExtensionBrowserTest5SetUpEv + 238
51  browser_tests                       0x000000010d934e03 _ZN15WebViewTestBase5SetUpEv + 387
52  browser_tests                       0x000000011436797e _ZN7testing8internal38HandleSehExceptionsInMethodIfSupportedINS_4TestEvEET0_PT_MS4_FS3_vEPKc + 126
53  browser_tests                       0x0000000114339942 _ZN7testing8internal35HandleExceptionsInMethodIfSupportedINS_4TestEvEET0_PT_MS4_FS3_vEPKc + 114
54  browser_tests                       0x0000000114339824 _ZN7testing4Test3RunEv + 116
55  browser_tests                       0x000000011433b82d _ZN7testing8TestInfo3RunEv + 221
56  browser_tests                       0x000000011433d26c _ZN7testing8TestCase3RunEv + 236
57  browser_tests                       0x0000000114352eda _ZN7testing8internal12UnitTestImpl11RunAllTestsEv + 922
58  browser_tests                       0x000000011436a98e _ZN7testing8internal38HandleSehExceptionsInMethodIfSupportedINS0_12UnitTestImplEbEET0_PT_MS4_FS3_vEPKc + 126
59  browser_tests                       0x0000000114352ac2 _ZN7testing8internal35HandleExceptionsInMethodIfSupportedINS0_12UnitTestImplEbEET0_PT_MS4_FS3_vEPKc + 114
60  browser_tests                       0x0000000114352999 _ZN7testing8UnitTest3RunEv + 393
61  browser_tests                       0x0000000111ef90f1 _Z13RUN_ALL_TESTSv + 17
[457/511] WebViewTests/WebViewTest.Shim_TestNestedSubframes/0 (TIMED OUT)

lazyboy@: assigning to you since you are one of the owner of the affected test. Please triage further if you're not the right owner for this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f3feff87ab751bde268b46426e779a89abd2da90

commit f3feff87ab751bde268b46426e779a89abd2da90
Author: guidou <guidou@chromium.org>
Date: Fri Dec 16 14:24:19 2016

Disable WebViewTest.Shim_TestNestedSubframes on Mac.

The test has been flaking on at least one Mac bot.

BUG=674904
TBR=lazyboy@chromium.org

Review-Url: https://codereview.chromium.org/2582023002
Cr-Commit-Position: refs/heads/master@{#439099}

[modify] https://crrev.com/f3feff87ab751bde268b46426e779a89abd2da90/chrome/browser/apps/guest_view/web_view_browsertest.cc

+James for triaging.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4f3b60632d6a987c009e8f56d57efa968a1806d7

commit 4f3b60632d6a987c009e8f56d57efa968a1806d7
Author: arthursonzogni <arthursonzogni@chromium.org>
Date: Fri Mar 09 08:33:55 2018

Fix flaky <webview> tests.

The two tests following tests are potentially flaky:
 * WebViewTests/WebViewTest.Shim_TestNestedSubframes/*
 * WebViewTests/WebViewTest.Shim_TestNestedCrossOriginSubframes/*

Why are they flaky?

webview.onloadstop event handler is defined. Once called, it causes a
new navigation to happens in the webview. The navigation causes the
handler to be called again. This is a loop. It wasn't expected to behave
that way.

If the nested iframe navigation happens quickly enough, the two time
nested iframe navigation might not complete quickly enough and the
postMessage() may not happens.

The race condition may be unfavourable several time in a row and causes
a test timeout.

FYI:
    1) This test was disabled on Mac. Maybe this CL fixes the issue? It
       should be verified on a device with this OS.
    2) This test is flakier after enabling NavigationMojoResponse and
       applying this CL:
       https://chromium-review.googlesource.com/c/chromium/src/+/951243/6
       That's understandable, this patch allows navigation to commit
       faster.

Bug: 674904,  705744 
Change-Id: Icf2debd095519221ff085cb3bacbc058c1806e86
Reviewed-on: https://chromium-review.googlesource.com/955585
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542064}
[modify] https://crrev.com/4f3b60632d6a987c009e8f56d57efa968a1806d7/chrome/test/data/extensions/platform_apps/web_view/shim/main.js