It started failing since https://ci.chromium.org/buildbot/chromium.chromiumos/chromeos-amd64-generic-rel/7951

Error messages:
FAILED: obj/chrome/browser/browser/about_flags.o 
/b/c/goma_client/gomacc x86_64-cros-linux-gnu-clang++ -B/b/c/b/chromeos_amd64_generic_rel/.cros_cache/chrome-sdk/tarballs/amd64-generic+10471.0.0+target_toolchain/usr/x86_64-pc-linux-gnu/x86_64-cros-linux-gnu/binutils-bin/2.27.0-gold -Wno-unknown-warning-option -MMD -MF obj/chrome/browser/browser/about_flags.o.d -DUSE_CRAS -DV8_DEPRECATION_WARNINGS -DUSE_UDEV -DUSE_AURA=1 -DUSE_NSS_CERTS=1 -DUSE_OZONE=1 -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DCHROMIUM_BUILD -DFIELDTRIAL_TESTING_ENABLED -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -DCR_CLANG_REVISION=\"325667-1\" -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -DOS_CHROMEOS -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -DUSE_CUPS -DWEBP_EXTERN=extern -DUSE_EGL -DTOOLKIT_VIEWS=1 -DEXPAT_RELATIVE_PATH -DU_USING_ICU_NAMESPACE=0 -DU_ENABLE_DYLOAD=0 -DU_STATIC_IMPLEMENTATION -DICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_FILE -DUCHAR_TYPE=uint16_t -DGOOGLE_PROTOBUF_NO_RTTI -DGOOGLE_PROTOBUF_NO_STATIC_INITIALIZER -DHAVE_PTHREAD -DV8_USE_EXTERNAL_STARTUP_DATA -DLEVELDB_PLATFORM_CHROMIUM=1 -DSK_IGNORE_LINEONLY_AA_CONVEX_PATH_OPTS -DSK_HAS_PNG_LIBRARY -DSK_HAS_WEBP_LIBRARY -DSK_HAS_JPEG_LIBRARY -DSK_SUPPORT_GPU=1 -DMESA_EGL_NO_X11_HEADERS -DI18N_ADDRESS_VALIDATION_DATA_URL=\"https://chromium-i18n.appspot.com/ssl-aggregate-address/\" -DWEBRTC_NON_STATIC_TRACE_EVENT_HANDLERS=0 -DGTEST_RELATIVE_PATH -DWEBRTC_CHROMIUM_BUILD -DWEBRTC_POSIX -DWEBRTC_LINUX -DCHROMEOS -D__CHROMEOS__ -DHUNSPELL_STATIC -DHUNSPELL_CHROME_CLIENT -DUSE_HUNSPELL -I../.. -Igen -I../../third_party/libwebp/src -I../../third_party/khronos -I../../gpu -I../../third_party/libyuv/include -I../../third_party/webrtc_overrides -I../../testing/gtest/include -I../../third_party/libyuv/include -I../../third_party/usrsctp/usrsctplib -I../../third_party/webrtc -I../../third_party/ced/src -I../../third_party/icu/source/common -I../../third_party/icu/source/i18n -I../../third_party/protobuf/src -I../../third_party/protobuf/src -Igen/protoc_out -I../../third_party/boringssl/src/include -I../../third_party/leveldatabase -I../../third_party/leveldatabase/src -I../../third_party/leveldatabase/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/libwebm/source -I../../third_party/WebKit -Igen/third_party/WebKit -I../../v8/include -Igen/v8/include -Igen/third_party/metrics_proto -I../../third_party/re2/src -I../../third_party/mesa/src/include -Igen -Igen -I../../third_party/libaddressinput/src/cpp/include -I../../third_party/webrtc_overrides -I../../third_party/webrtc -I../../third_party/cacheinvalidation/overrides -I../../third_party/cacheinvalidation/src -I../../third_party/libxml/src/include -I../../third_party/libxml/linux/include -I../../third_party/zlib -I../../third_party/breakpad/breakpad/src -Igen -I../../third_party/webrtc_overrides -I../../testing/gtest/include -I../../third_party/webrtc -fno-strict-aliasing -Wno-builtin-macro-redefined -D__DATE__= -D__TIME__= -D__TIMESTAMP__= -funwind-tables -fPIC -pipe -B../../third_party/binutils/Linux_x64/Release/bin -pthread -fcolor-diagnostics -no-canonical-prefixes -m64 -march=x86-64 -Wall -Wextra -Wimplicit-fallthrough -Wthread-safety -Wno-missing-field-initializers -Wno-unused-parameter -Wno-c++11-narrowing -Wno-covered-switch-default -Wno-unneeded-internal-declaration -Wno-inconsistent-missing-override -Wno-undefined-var-template -Wno-nonportable-include-path -Wno-address-of-packed-member -Wno-unused-lambda-capture -Wno-user-defined-warnings -Wno-enum-compare-switch -Wno-null-pointer-arithmetic -O2 -fno-ident -fdata-sections -ffunction-sections -fno-omit-frame-pointer -g2 -gsplit-dwarf -ggnu-pubnames -fvisibility=hidden -Wheader-hygiene -Wstring-conversion -Wtautological-overlap-compare -Wexit-time-destructors -Wno-header-guard -isystem/b/c/b/chromeos_amd64_generic_rel/.cros_cache/chrome-sdk/tarballs/amd64-generic+10471.0.0+sysroot_chromeos-base_chromeos-chrome.tar.xz/usr/include/nss -isystem/b/c/b/chromeos_amd64_generic_rel/.cros_cache/chrome-sdk/tarballs/amd64-generic+10471.0.0+sysroot_chromeos-base_chromeos-chrome.tar.xz/usr/include/nspr -isystem/b/c/b/chromeos_amd64_generic_rel/.cros_cache/chrome-sdk/tarballs/amd64-generic+10471.0.0+sysroot_chromeos-base_chromeos-chrome.tar.xz/usr/include/dbus-1.0 -isystem/b/c/b/chromeos_amd64_generic_rel/.cros_cache/chrome-sdk/tarballs/amd64-generic+10471.0.0+sysroot_chromeos-base_chromeos-chrome.tar.xz/usr/lib64/dbus-1.0/include -DLIBXML_STATIC= -std=gnu++14 -fno-exceptions -fno-rtti --sysroot=../../../.cros_cache/chrome-sdk/tarballs/amd64-generic+10471.0.0+sysroot_chromeos-base_chromeos-chrome.tar.xz -fvisibility-inlines-hidden -pipe -pipe -pipe -march=x86-64 -msse3 -fno-split-dwarf-inlining -fdebug-info-for-profiling -D__google_stl_debug_vector=1 -Wno-unknown-warning-option -stdlib=libc++ -Wno-inline-asm -c ../../chrome/browser/about_flags.cc -o obj/chrome/browser/browser/about_flags.o
../../chrome/browser/about_flags.cc:3755:35: error: no member named 'kPdfIsolation' in namespace 'features'
     FEATURE_VALUE_TYPE(features::kPdfIsolation)},
                        ~~~~~~~~~~^
../../components/flags_ui/feature_entry_macros.h:34:8: note: expanded from macro 'FEATURE_VALUE_TYPE'
      &feature, 3, nullptr, nullptr, nullptr
       ^~~~~~~
../../chrome/browser/about_flags.cc:3766:39: error: no matching function for call to 'ArraySizeHelper'
      : flags_state_(kFeatureEntries, arraysize(kFeatureEntries)) {}
                                      ^~~~~~~~~~~~~~~~~~~~~~~~~~
../../base/macros.h:54:34: note: expanded from macro 'arraysize'
#define arraysize(array) (sizeof(ArraySizeHelper(array)))
                                 ^~~~~~~~~~~~~~~
../../base/macros.h:53:40: note: candidate template ignored: could not match 'T [N]' against 'const flags_ui::FeatureEntry []'
template <typename T, size_t N> char (&ArraySizeHelper(T (&array)[N]))[N];
                                       ^
../../chrome/browser/about_flags.cc:3949:12: error: no matching function for call to 'ArraySizeHelper'
  *count = arraysize(kFeatureEntries);
           ^~~~~~~~~~~~~~~~~~~~~~~~~~
../../base/macros.h:54:34: note: expanded from macro 'arraysize'
#define arraysize(array) (sizeof(ArraySizeHelper(array)))
                                 ^~~~~~~~~~~~~~~
../../base/macros.h:53:40: note: candidate template ignored: could not match 'T [N]' against 'const flags_ui::FeatureEntry []'
template <typename T, size_t N> char (&ArraySizeHelper(T (&array)[N]))[N];
                                       ^
3 errors generated.

Suspicious CL: https://chromium-review.googlesource.com/c/chromium/src/+/956488

tsepez@, please take a look.