[125881:125881:0713/154001.365246:1485507152498:FATAL:begin_frame_source.cc(288)] Check failed: observers_.empty(). 
#0 0x000000d7f09c base::debug::StackTrace::StackTrace()
#1 0x000000d1caab logging::LogMessage::~LogMessage()
#2 0x000000e7e3c1 viz::ExternalBeginFrameSource::~ExternalBeginFrameSource()
#3 0x000000e7e42e viz::ExternalBeginFrameSource::~ExternalBeginFrameSource()
#4 0x0000005c8061 viz::(anonymous namespace)::ExternalBeginFrameSourceTest_GetMissedBeginFrameArgs_Test::~ExternalBeginFrameSourceTest_GetMissedBeginFrameArgs_Test()
#5 0x0000009e01ed testing::TestInfo::Run()
#6 0x0000009e06a7 testing::TestCase::Run()
#7 0x0000009ebfa7 testing::internal::UnitTestImpl::RunAllTests()
#8 0x0000009ebb1d testing::UnitTest::Run()
#9 0x000000d942c1 base::TestSuite::Run()
#10 0x000000d9677d base::(anonymous namespace)::LaunchUnitTestsInternal()
#11 0x000000d965d1 base::LaunchUnitTests()
#12 0x00000059b1b6 main
#13 0x7f22e10e32b1 __libc_start_main
#14 0x00000059b02a _start

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a7c39a1d8b4e16e870b0dfdcff3f05f48e31f585

commit a7c39a1d8b4e16e870b0dfdcff3f05f48e31f585
Author: Greg Kraynov <kraynov@chromium.org>
Date: Fri Jul 13 17:35:34 2018

Restore and repair BeginFrameSource tests.

It was missed from BUILD.gn during the move from //cc.
Three tests are broken and were disabled, see bug for details.

Bug: 863422
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel
Change-Id: I83381ee2063b3c826a9923db98a5802eb6130db2
Reviewed-on: https://chromium-review.googlesource.com/1136548
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: Greg Kraynov <kraynov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574965}
[modify] https://crrev.com/a7c39a1d8b4e16e870b0dfdcff3f05f48e31f585/components/viz/common/BUILD.gn
[modify] https://crrev.com/a7c39a1d8b4e16e870b0dfdcff3f05f48e31f585/components/viz/common/frame_sinks/begin_frame_source_unittest.cc