UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.109 Safari/537.36

Example URL:
http://webaudiodemos.appspot.com/MIDIDrums/index.html

Steps to reproduce the problem:
1. Go to http://webaudiodemos.appspot.com/MIDIDrums/index.html
2. Press the Play icon
3. Close the tab

What is the expected behavior?
No crash.

What went wrong?
There is a NOTREACHED failure with this error:

[64990:34819:0626/133125.039874:FATAL:thread_restrictions.cc(38)] Check failed: false. Function marked as IO-only was called from a thread that disallows IO!  If this thread really should be allowed to make IO calls, adjust the call to base::ThreadRestrictions::SetIOAllowed() in this thread's startup.  If this task is running inside the TaskScheduler, the TaskRunner used to post it needs to have MayBlock() in its TaskTraits.
0   libbase.dylib                       0x000000010f5e38de base::debug::StackTrace::StackTrace(unsigned long) + 174
1   libbase.dylib                       0x000000010f5e397d base::debug::StackTrace::StackTrace(unsigned long) + 29
2   libbase.dylib                       0x000000010f5e1e0c base::debug::StackTrace::StackTrace() + 28
3   libbase.dylib                       0x000000010f6814cf logging::LogMessage::~LogMessage() + 479
4   libbase.dylib                       0x000000010f67ee45 logging::LogMessage::~LogMessage() + 21
5   libbase.dylib                       0x000000010f8e9a48 base::ThreadRestrictions::AssertIOAllowed() + 168
6   libbase.dylib                       0x000000010f8b061b base::PlatformThread::Join(base::PlatformThreadHandle) + 59
7   libbase.dylib                       0x000000010f8da0d1 base::Thread::Stop() + 305
8   libmidi.dylib                       0x000000013ebb94ec midi::MidiManagerMac::Finalize() + 44
9   libmidi.dylib                       0x000000013ebab6b5 midi::MidiManager::ShutdownOnSessionThread() + 69
10  libmidi.dylib                       0x000000013ebab560 midi::MidiManager::Shutdown() + 592
11  libmidi.dylib                       0x000000013ebd7099 midi::MidiService::EndSession(midi::MidiManagerClient*) + 457
12  libcontent.dylib                    0x0000000131c14821 content::MidiHost::OnChannelClosing() + 65
13  libcontent.dylib                    0x000000012fb65b2c content::BrowserMessageFilter::Internal::OnChannelClosing() + 76
14  libipc.dylib                        0x00000001149fd4f8 IPC::ChannelProxy::Context::OnChannelClosed() + 1224
15  libipc.dylib                        0x0000000114a03b5f void base::internal::FunctorTraits<void (IPC::ChannelProxy::Context::*)(), void>::Invoke<scoped_refptr<IPC::ChannelProxy::Context> const&>(void (IPC::ChannelProxy::Context::*)(), scoped_refptr<IPC::ChannelProxy::Context> const&&&) + 127
16  libipc.dylib                        0x0000000114a03ad4 void base::internal::InvokeHelper<false, void>::MakeItSo<void (IPC::ChannelProxy::Context::* const&)(), scoped_refptr<IPC::ChannelProxy::Context> const&>(void (IPC::ChannelProxy::Context::* const&&&)(), scoped_refptr<IPC::ChannelProxy::Context> const&&&) + 68
17  libipc.dylib                        0x0000000114a03a80 void base::internal::Invoker<base::internal::BindState<void (IPC::ChannelProxy::Context::*)(), scoped_refptr<IPC::ChannelProxy::Context> >, void ()>::RunImpl<void (IPC::ChannelProxy::Context::* const&)(), std::__1::tuple<scoped_refptr<IPC::ChannelProxy::Context> > const&, 0ul>(void (IPC::ChannelProxy::Context::* const&&&)(), std::__1::tuple<scoped_refptr<IPC::ChannelProxy::Context> > const&&&, base::IndexSequence<0ul>) + 80
18  libipc.dylib                        0x0000000114a039cc base::internal::Invoker<base::internal::BindState<void (IPC::ChannelProxy::Context::*)(), scoped_refptr<IPC::ChannelProxy::Context> >, void ()>::Run(base::internal::BindStateBase*) + 44
19  libbase.dylib                       0x000000010f5812ef base::Callback<void (), (base::internal::CopyMode)0, (base::internal::RepeatMode)0>::Run() + 95
20  libbase.dylib                       0x000000010f5e5e20 base::debug::TaskAnnotator::RunTask(char const*, base::PendingTask*) + 1024
21  libbase.dylib                       0x000000010f6de00e base::MessageLoop::RunTask(base::PendingTask*) + 894
22  libbase.dylib                       0x000000010f6de567 base::MessageLoop::DeferOrRunPendingTask(base::PendingTask) + 71
23  libbase.dylib                       0x000000010f6df44b base::MessageLoop::DoWork() + 715
24  libbase.dylib                       0x000000010f6ed11f base::MessagePumpLibevent::Run(base::MessagePump::Delegate*) + 271
25  libbase.dylib                       0x000000010f6dd8cb base::MessageLoop::Run() + 299
26  libbase.dylib                       0x000000010f7d125e base::RunLoop::Run() + 286
27  libbase.dylib                       0x000000010f8dba25 base::Thread::Run(base::RunLoop*) + 405
28  libcontent.dylib                    0x0000000131149d77 content::BrowserThreadImpl::IOThreadRun(base::RunLoop*) + 71
29  libcontent.dylib                    0x000000013114a07c content::BrowserThreadImpl::Run(base::RunLoop*) + 588
30  libbase.dylib                       0x000000010f8dc7e3 base::Thread::ThreadMain() + 2403
31  libbase.dylib                       0x000000010f8b0b78 base::(anonymous namespace)::ThreadFunc(void*) + 632
32  libsystem_pthread.dylib             0x00007fffd37f093b _pthread_body + 180
33  libsystem_pthread.dylib             0x00007fffd37f0887 _pthread_body + 0
34  libsystem_pthread.dylib             0x00007fffd37f008d thread_start + 13

Did this work before? Yes 59.0.3071.109

Is it a problem with Flash or HTML5? HTML5

Does this work in other browsers? Yes

Chrome version: 61.0.3142.0  Channel: canary
OS Version: OS X 10.12.5
Flash Version: 

Contents of chrome://gpu: 
Note: To properly save this page, select the "Webpage, Complete" option in the Save File dialog.
Graphics Feature Status
Canvas: Hardware accelerated
CheckerImaging: Enabled
Flash: Hardware accelerated
Flash Stage3D: Hardware accelerated
Flash Stage3D Baseline profile: Hardware accelerated
Compositing: Hardware accelerated
Multiple Raster Threads: Enabled
Native GpuMemoryBuffers: Hardware accelerated
Rasterization: Hardware accelerated
Video Decode: Hardware accelerated
Video Encode: Hardware accelerated
WebGL: Hardware accelerated
WebGL2: Hardware accelerated
Driver Bug Workarounds
adjust_src_dst_region_for_blitframebuffer
decode_encode_srgb_for_generatemipmap
disable_framebuffer_cmaa
disable_multimonitor_multisampling
get_frag_data_info_bug
pack_parameters_workaround_with_pack_buffer
regenerate_struct_names
remove_invariant_and_centroid_for_essl3
scalarize_vec_and_mat_constructor_args
set_zero_level_before_generating_mipmap
unfold_short_circuit_as_ternary_operation
unpack_alignment_workaround_with_unpack_buffer
use_intermediary_for_copy_texture_image
use_unused_standard_shared_blocks
Problems Detected
Multisampling is buggy on OSX when multiple monitors are connected: 237931
Applied Workarounds: disable_multimonitor_multisampling
Unfold short circuit on Mac OS X: 307751
Applied Workarounds: unfold_short_circuit_as_ternary_operation
Always rewrite vec/mat constructors to be consistent: 398694
Applied Workarounds: scalarize_vec_and_mat_constructor_args
Mac drivers handle struct scopes incorrectly: 403957
Applied Workarounds: regenerate_struct_names
glGenerateMipmap fails if the zero texture level is not set on some Mac drivers: 560499
Applied Workarounds: set_zero_level_before_generating_mipmap
Pack parameters work incorrectly with pack buffer bound: 563714
Applied Workarounds: pack_parameters_workaround_with_pack_buffer
Alignment works incorrectly with unpack buffer bound: 563714
Applied Workarounds: unpack_alignment_workaround_with_unpack_buffer
copyTexImage2D fails when reading from IOSurface on multiple GPU types.: 581777
Applied Workarounds: use_intermediary_for_copy_texture_image
Limited enabling of Chromium GL_INTEL_framebuffer_CMAA: 535198
Applied Workarounds: disable_framebuffer_cmaa
glGetFragData{Location|Index} works incorrectly on Max: 638340
Applied Workarounds: get_frag_data_info_bug
Decode and encode before generateMipmap for srgb format textures on macosx: 634519
Applied Workarounds: decode_encode_srgb_for_generatemipmap
Insert statements to reference all members in unused std140/shared blocks on Mac: 618464
Applied Workarounds: use_unused_standard_shared_blocks
adjust src/dst region if blitting pixels outside read framebuffer on Mac: 644740
Applied Workarounds: adjust_src_dst_region_for_blitframebuffer
Mac driver GL 4.1 requires invariant and centroid to match between shaders: 639760, 641129
Applied Workarounds: remove_invariant_and_centroid_for_essl3
Disable KHR_blend_equation_advanced until cc shaders are updated: 661715
Version Information
Data exported	6/26/2017, 1:34:03 PM
Chrome version	Chrome/61.0.3142.0
Operating system	Mac OS X 10.12.5
Software rendering list version	13.8
Driver bug list version	10.16
ANGLE commit id	579d8c7dfcfa
2D graphics backend	Skia/61 df669811b16e317b307b335822c4c7c881c1d163-
Command Line	./out/Default/Chromium.app/Contents/MacOS/Chromium --flag-switches-begin --flag-switches-end
Driver Information
Initialization time	44
In-process GPU	false
Passthrough Command Decoder	false
Supports overlays	false
Sandboxed	true
GPU0	VENDOR = 0x1002, DEVICE= 0x6821 *ACTIVE*
GPU1	VENDOR = 0x8086, DEVICE= 0x0d26
Optimus	false
Optimus	false
AMD switchable	true
Driver vendor	
Driver version	1.51.8
Driver date	
Pixel shader version	4.10
Vertex shader version	4.10
Max. MSAA samples	8
Machine model name	MacBookPro
Machine model version	11.5
GL_VENDOR	ATI Technologies Inc.
GL_RENDERER	AMD Radeon R9 M370X OpenGL Engine
GL_VERSION	4.1 ATI-1.51.8
GL_EXTENSIONS	GL_ARB_blend_func_extended GL_ARB_draw_buffers_blend GL_ARB_draw_indirect GL_ARB_ES2_compatibility GL_ARB_explicit_attrib_location GL_ARB_gpu_shader_fp64 GL_ARB_gpu_shader5 GL_ARB_instanced_arrays GL_ARB_internalformat_query GL_ARB_occlusion_query2 GL_ARB_sample_shading GL_ARB_sampler_objects GL_ARB_separate_shader_objects GL_ARB_shader_bit_encoding GL_ARB_shader_subroutine GL_ARB_shading_language_include GL_ARB_tessellation_shader GL_ARB_texture_buffer_object_rgb32 GL_ARB_texture_cube_map_array GL_ARB_texture_gather GL_ARB_texture_query_lod GL_ARB_texture_rgb10_a2ui GL_ARB_texture_storage GL_ARB_texture_swizzle GL_ARB_timer_query GL_ARB_transform_feedback2 GL_ARB_transform_feedback3 GL_ARB_vertex_attrib_64bit GL_ARB_vertex_type_2_10_10_10_rev GL_ARB_viewport_array GL_EXT_debug_label GL_EXT_debug_marker GL_EXT_depth_bounds_test GL_EXT_texture_compression_s3tc GL_EXT_texture_filter_anisotropic GL_EXT_texture_mirror_clamp GL_EXT_texture_sRGB_decode GL_APPLE_client_storage GL_APPLE_container_object_shareable GL_APPLE_flush_render GL_APPLE_object_purgeable GL_APPLE_rgb_422 GL_APPLE_row_bytes GL_APPLE_texture_range GL_ATI_texture_mirror_once GL_NV_texture_barrier
Disabled Extensions	GL_KHR_blend_equation_advanced GL_KHR_blend_equation_advanced_coherent
Window system binding vendor	
Window system binding version	
Window system binding extensions	
Direct rendering	Yes
Reset notification strategy	0x0000
GPU process crash count	0
Compositor Information
Tile Update Mode	Zero-copy
Partial Raster	Enabled
GpuMemoryBuffers Status
ATC	Software only
ATCIA	Software only
DXT1	Software only
DXT5	Software only
ETC1	Software only
R_8	GPU_READ_CPU_READ_WRITE, GPU_READ_CPU_READ_WRITE_PERSISTENT
R_16	Software only
RG_88	Software only
BGR_565	Software only
RGBA_4444	Software only
RGBX_8888	Software only
RGBA_8888	GPU_READ, SCANOUT, SCANOUT_CPU_READ_WRITE
BGRX_8888	GPU_READ, SCANOUT, SCANOUT_CPU_READ_WRITE
BGRA_8888	GPU_READ, SCANOUT, SCANOUT_CPU_READ_WRITE, GPU_READ_CPU_READ_WRITE, GPU_READ_CPU_READ_WRITE_PERSISTENT
RGBA_F16	GPU_READ_CPU_READ_WRITE, GPU_READ_CPU_READ_WRITE_PERSISTENT
YVU_420	Software only
YUV_420_BIPLANAR	GPU_READ_CPU_READ_WRITE, GPU_READ_CPU_READ_WRITE_PERSISTENT
UYVY_422	GPU_READ_CPU_READ_WRITE, GPU_READ_CPU_READ_WRITE_PERSISTENT

The NOTREACHED is from a local debug build, in Canary there is a crash on certain WebMIDI pages. I am assuming that the root cause of the crash in the Release build is this NOTREACHED failure but have not verified this.