Cancelling builds that started prior to https://chromium.googlesource.com/chromium/src.git/+/25eb9e4d58709999fcb50219a4dc1b44b49b7256

A subset of mac_chromium_rel_ng bots also seem to be experiencing goma issues; failures look like

[280/54904] CXX obj/base/base/process_metrics.o
FAILED: obj/base/base/process_metrics.o 
export DEVELOPER_DIR=/b/s/w/ir/cache/builder/src/build/mac_files/Xcode.app;  /b/s/w/ir/cache/goma/client/gomacc ../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF obj/base/base/process_metrics.o.d -DSYSTEM_NATIVE_UTF8 -DV8_DEPRECATION_WARNINGS -DDCHECK_ALWAYS_ON=1 -DNO_TCMALLOC -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DCHROMIUM_BUILD -DFIELDTRIAL_TESTING_ENABLED -D_LIBCPP_HAS_NO_ALIGNED_ALLOCATION -DCR_XCODE_VERSION=0832 -DCR_CLANG_REVISION=\"344066-1\" -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D_FORTIFY_SOURCE=2 -D__ASSERT_MACROS_DEFINE_VERSIONS_WITHOUT_UNDERSCORE=0 -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -DBASE_IMPLEMENTATION -I../.. -Igen -fno-strict-aliasing -fstack-protector -Wno-builtin-macro-redefined -D__DATE__= -D__TIME__= -D__TIMESTAMP__= -fcolor-diagnostics -fmerge-all-constants -Xclang -mllvm -Xclang -instcombine-lower-dbg-declare=0 -no-canonical-prefixes -arch x86_64 -Wall -Werror -Wextra -Wimplicit-fallthrough -Wthread-safety -Wunguarded-availability -Wno-missing-field-initializers -Wno-unused-parameter -Wno-c++11-narrowing -Wno-unneeded-internal-declaration -Wno-undefined-var-template -Wno-null-pointer-arithmetic -Wno-ignored-pragma-optimize -Wno-defaulted-function-deleted -fno-omit-frame-pointer -g1 -isysroot ../../build/mac_files/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk -mmacosx-version-min=10.9.0 -fvisibility=hidden -Xclang -load -Xclang ../../third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.dylib -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-char-subscripts -Wglobal-constructors -Wexit-time-destructors -Wshadow -Wexit-time-destructors -O2 -std=c++14 -stdlib=libc++ -fno-exceptions -fno-rtti -fvisibility-inlines-hidden -c ../../base/process/process_metrics.cc -o obj/base/base/process_metrics.o
E1024 11:21:10.804611 2633696064 goma_ipc.cc:235] GOMA: Unexpected end-of-file at 0+32768: No such process
E1024 11:21:10.817325 2633696064 gomacc.cc:401] GOMA: compiler proxy not working?

#2 looks like it may have been limited to vm258-m4. The builder was missing everything but clang from third_party/llvm-build/Release+Asserts/bin/, which caused difficult-to-parse goma errors.

Will file a follow up to either detect or recover from similar issues.