This bot started failing at this build:

https://build.chromium.org/p/chromium.gpu.fyi/builders/GPU%20Win%20Clang%20Builder%20%28dbg%29/builds/16743

With the following error:

[1335/5118] LINK media_unittests.exe media_unittests.exe.pdb
FAILED: media_unittests.exe media_unittests.exe.pdb 
E:/b/depot_tools/win_tools-2_7_6_bin/python/bin/python.exe ../../build/toolchain/win/tool_wrapper.py link-wrapper environment.x64 False link.exe /nologo /OUT:./media_unittests.exe /PDB:./media_unittests.exe.pdb @./media_unittests.exe.rsp
source_buffer_stream_unittest.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: void __cdecl media::SourceBufferStream<class media::SourceBufferRangeByDts>::OnStartOfCodedFrameGroup(class media::DecodeTimestamp,class base::TimeDelta)" (__imp_?OnStartOfCodedFrameGroup@?$SourceBufferStream@VSourceBufferRangeByDts@media@@@media@@QEAAXVDecodeTimestamp@2@VTimeDelta@base@@@Z) referenced in function "public: virtual void __cdecl media::SourceBufferStreamTest_Audio_SpliceTrimming_ExistingTrimming_Test::TestBody(void)" (?TestBody@SourceBufferStreamTest_Audio_SpliceTrimming_ExistingTrimming_Test@media@@UEAAXXZ)
source_buffer_stream_unittest.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: void __cdecl media::SourceBufferStream<class media::SourceBufferRangeByPts>::OnStartOfCodedFrameGroup(class media::DecodeTimestamp,class base::TimeDelta)" (__imp_?OnStartOfCodedFrameGroup@?$SourceBufferStream@VSourceBufferRangeByPts@media@@@media@@QEAAXVDecodeTimestamp@2@VTimeDelta@base@@@Z) referenced in function "public: virtual void __cdecl media::SourceBufferStreamTest_Audio_SpliceTrimming_ExistingTrimming_Test::TestBody(void)" (?TestBody@SourceBufferStreamTest_Audio_SpliceTrimming_ExistingTrimming_Test@media@@UEAAXXZ)
./media_unittests.exe : fatal error LNK1120: 2 unresolved externals

Matt: Your CL https://chromium-review.googlesource.com/c/chromium/src/+/678443 is in the regression range and looks very related, can you take a look?