We've seen the tree being closed, apparently due to missing DEPs, e.g. [1] which fails with:

FAILED: obj/headless/headless/headless_devtools_session.obj 
C:\b\swarming\w\ir\cache\goma\client/gomacc.exe ../../third_party/llvm-build/Release+Asserts/bin/clang-cl.exe /nologo /showIncludes  -imsvc..\..\..\..\win_toolchain\vs_files\3bc0ec615cf20ee342f3bc29bc991b5ad66d8d2c\win_sdk\Include\10.0.17134.0\um -imsvc..\..\..\..\win_toolchain\vs_files\3bc0ec615cf20ee342f3bc29bc991b5ad66d8d2c\win_sdk\Include\10.0.17134.0\shared -imsvc..\..\..\..\win_toolchain\vs_files\3bc0ec615cf20ee342f3bc29bc991b5ad66d8d2c\win_sdk\Include\10.0.17134.0\winrt -imsvc..\..\..\..\win_toolchain\vs_files\3bc0ec615cf20ee342f3bc29bc991b5ad66d8d2c\win_sdk\Include\10.0.17134.0\ucrt -imsvc..\..\..\..\win_toolchain\vs_files\3bc0ec615cf20ee342f3bc29bc991b5ad66d8d2c\VC\Tools\MSVC\14.14.26428\include -imsvc..\..\..\..\win_toolchain\vs_files\3bc0ec615cf20ee342f3bc29bc991b5ad66d8d2c\VC\Tools\MSVC\14.14.26428\atlmfc\include -DV8_DEPRECATION_WARNINGS -DUSE_AURA=1 -DNO_TCMALLOC -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DCHROMIUM_BUILD -DFIELDTRIAL_TESTING_ENABLED "-DCR_CLANG_REVISION=\"336424-1\"" -D_HAS_NODISCARD -D_HAS_EXCEPTIONS=0 -D__STD_C -D_CRT_RAND_S -D_CRT_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_DEPRECATE -D_ATL_NO_OPENGL -D_WINDOWS -DCERT_CHAIN_PARA_HAS_EXTRA_FIELDS -DPSAPI_VERSION=1 -DWIN32 -D_SECURE_ATL -D_USING_V110_SDK71_ -DWINAPI_FAMILY=WINAPI_FAMILY_DESKTOP_APP -DWIN32_LEAN_AND_MEAN -DNOMINMAX -D_UNICODE -DUNICODE -DNTDDI_VERSION=0x0A000002 -D_WIN32_WINNT=0x0A00 -DWINVER=0x0A00 -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -DHEADLESS_IMPLEMENTATION -DWEBP_EXTERN=extern -DENABLE_IPC_FUZZER -DUSE_EGL -DGOOGLE_PROTOBUF_NO_RTTI -DGOOGLE_PROTOBUF_NO_STATIC_INITIALIZER -DSK_IGNORE_LINEONLY_AA_CONVEX_PATH_OPTS -DSK_HAS_PNG_LIBRARY -DSK_HAS_WEBP_LIBRARY -DSK_HAS_JPEG_LIBRARY -DSK_SUPPORT_GPU=1 "-DSK_GPU_WORKAROUNDS_HEADER=\"gpu/config/gpu_driver_bug_workaround_autogen.h\"" -DGR_GL_FUNCTION_TYPE=__stdcall -DV8_USE_EXTERNAL_STARTUP_DATA -DU_USING_ICU_NAMESPACE=0 -DU_ENABLE_DYLOAD=0 -DU_STATIC_IMPLEMENTATION -DICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_FILE -DUCHAR_TYPE=wchar_t -DLEVELDB_PLATFORM_CHROMIUM=1 -DDeleteFile=DeleteFileW -DOS_WIN -DWEBRTC_NON_STATIC_TRACE_EVENT_HANDLERS=0 -DGTEST_RELATIVE_PATH -DWEBRTC_CHROMIUM_BUILD -DWEBRTC_WIN -DABSL_ALLOCATOR_NOTHROW=1 -DNO_MAIN_THREAD_WRAPPING -I../.. -Igen -I../../third_party/libwebp/src -I../../third_party/wtl/include -I../../third_party/libyuv/include -I../../third_party/khronos -I../../gpu -I../../third_party/protobuf/src -Igen/protoc_out -I../../third_party/protobuf/src -I../../third_party/boringssl/src/include -I../../skia/config -I../../skia/ext -I../../third_party/skia/include/c -I../../third_party/skia/include/config -I../../third_party/skia/include/core -I../../third_party/skia/include/effects -I../../third_party/skia/include/encode -I../../third_party/skia/include/gpu -I../../third_party/skia/include/images -I../../third_party/skia/include/lazy -I../../third_party/skia/include/pathops -I../../third_party/skia/include/pdf -I../../third_party/skia/include/pipe -I../../third_party/skia/include/ports -I../../third_party/skia/include/utils -I../../third_party/skia/src/gpu -I../../third_party/skia/src/sksl -I../../third_party/ced/src -I../../third_party/icu/source/common -I../../third_party/icu/source/i18n -I../../third_party/leveldatabase -I../../third_party/leveldatabase/src -I../../third_party/leveldatabase/src/include -I../../third_party/libwebm/source -I../../v8/include -Igen/v8/include -I../../third_party/webrtc_overrides -I../../third_party/webrtc /utf-8 /X -Wno-builtin-macro-redefined -D__DATE__= -D__TIME__= -D__TIMESTAMP__= -fcolor-diagnostics -fmerge-all-constants -Xclang -mllvm -Xclang -instcombine-lower-dbg-declare=0 -Xclang -fdebug-compilation-dir -Xclang . -no-canonical-prefixes -fcomplete-member-pointers /Gy /FS /bigobj /d2FastFail /Zc:sizedDealloc- -fmsc-version=1911 -m64 /Brepro /W4 -Wimplicit-fallthrough -Wthread-safety /WX /wd4091 /wd4127 /wd4251 /wd4275 /wd4312 /wd4324 /wd4351 /wd4355 /wd4503 /wd4589 /wd4611 /wd4100 /wd4121 /wd4244 /wd4505 /wd4510 /wd4512 /wd4610 /wd4838 /wd4995 /wd4996 /wd4456 /wd4457 /wd4458 /wd4459 /wd4200 /wd4201 /wd4204 /wd4221 /wd4018 /wd4245 /wd4267 /wd4305 /wd4389 /wd4702 /wd4701 /wd4703 /wd4661 /wd4706 /wd4715 -Wno-missing-field-initializers -Wno-unused-parameter -Wno-c++11-narrowing -Wno-covered-switch-default -Wno-unneeded-internal-declaration -Wno-undefined-var-template -Wno-address-of-packed-member -Wno-nonportable-include-path -Wno-user-defined-warnings -Wno-unused-lambda-capture -Wno-null-pointer-arithmetic -Wno-enum-compare-switch -Wno-ignored-pragma-optimize /O1 /Ob2 /Oy- /Zc:inline /Gw /Oi /MT -Xclang -add-plugin -Xclang find-bad-constructs -Xclang -plugin-arg-find-bad-constructs -Xclang enforce-in-thirdparty-webkit -Xclang -plugin-arg-find-bad-constructs -Xclang check-enum-max-value -Wheader-hygiene -Wstring-conversion -Wtautological-overlap-compare -Wno-inconsistent-missing-override /wd4267 -imsvc ../../third_party/abseil-cpp /TP /wd4577 /GR- /c ../../headless/lib/browser/protocol/headless_devtools_session.cc /Foobj/headless/headless/headless_devtools_session.obj /Fd"obj/headless/headless_cc.pdb"
In file included from ../../headless/lib/browser/protocol/headless_devtools_session.cc:12:
../..\headless/lib/browser/protocol/page_handler.h(10,10):  fatal error: 'printing/buildflags/buildflags.h' file not found
#include "printing/buildflags/buildflags.h"
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

[1] https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8940757182692637712/+/steps/compile/0/stdout