First failing build:
https://build.chromium.org/p/chromium.gpu.fyi/builders/GPU%20Win%20Clang%20Builder%20%28dbg%29/builds/3530

Suspecting this to be r390494: "Verify that Update 2 of VS 2015 is used to build Chromium"

Adding jmadill to see if there is an easy fix by just removing the fields.

Adding brucedawson to verify that this is the likely reason for this Windows-only compile failure.

Compile failure:
FAILED: obj/third_party/angle/src/libANGLE/renderer/d3d/d3d11/libANGLE.TextureStorage11.obj 
ninja -t msvc -e environment.x86 -- E:\b\build\slave\cache\cipd\goma/gomacc "..\..\third_party/llvm-build/Release+Asserts/bin/clang-cl" -m32 /nologo /showIncludes /FC @obj\third_party\angle\src\libANGLE\renderer\d3d\d3d11\libANGLE.TextureStorage11.obj.rsp /c ..\..\third_party\angle\src\libANGLE\renderer\d3d\d3d11\TextureStorage11.cpp /Foobj\third_party\angle\src\libANGLE\renderer\d3d\d3d11\libANGLE.TextureStorage11.obj /Fdobj\third_party\angle\src\libANGLE.cc.pdb 
In file included from ..\..\third_party\angle\src\libANGLE\renderer\d3d\d3d11\TextureStorage11.cpp:11:
..\..\third_party\angle\src\libANGLE/renderer/d3d/d3d11/TextureStorage11.h(237,9):  error: private field 'mPlaneIndex' is not used [-Werror,-Wunused-private-field]
    int mPlaneIndex;
        ^
..\..\third_party\angle\src\libANGLE/renderer/d3d/d3d11/TextureStorage11.h(241,22):  error: private field 'mSwizzleTexture' is not used [-Werror,-Wunused-private-field]
    ID3D11Texture2D *mSwizzleTexture;
                     ^
..\..\third_party\angle\src\libANGLE/renderer/d3d/d3d11/TextureStorage11.h(242,29):  error: private field 'mSwizzleRenderTarget' is not used [-Werror,-Wunused-private-field]
    ID3D11RenderTargetView *mSwizzleRenderTarget;
                            ^