Version: master
OS: OSX 10.12 Beta (16A294a)

What steps will reproduce the problem?
(1) Get OSX 10.12 and XCode 8 beta 6
(2) ninja -C out/Default chrome

What is the expected output?

Successful build.

What do you see instead?

FAILED: obj/content/browser/browser/browser_accessibility_cocoa.o 
../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF obj/content/browser/browser/browser_accessibility_cocoa.o.d -DENABLE_SCREEN_CAPTURE=1 -DV8_DEPRECATION_WARNINGS -DENABLE_NOTIFICATIONS -DENABLE_PEPPER_CDMS -DENABLE_PLUGINS=1 -DENABLE_PDF=1 -DENABLE_PRINTING=1 -DENABLE_BASIC_PRINTING=1 -DENABLE_PRINT_PREVIEW=1 -DENABLE_SPELLCHECK=1 -DUSE_BROWSER_SPELLCHECKER=1 -DNO_TCMALLOC -DUSE_EXTERNAL_POPUP_MENU=1 -DENABLE_WEBRTC=1 -DENABLE_EXTENSIONS=1 -DENABLE_TASK_MANAGER=1 -DENABLE_THEMES=1 -DENABLE_CAPTIVE_PORTAL_DETECTION=1 -DENABLE_SESSION_SERVICE=1 -DENABLE_PLUGIN_INSTALLATION=1 -DENABLE_SUPERVISED_USERS=1 -DENABLE_SERVICE_DISCOVERY=1 -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DCHROMIUM_BUILD -DENABLE_MEDIA_ROUTER=1 -DFIELDTRIAL_TESTING_ENABLED -DCR_CLANG_REVISION=277962-1 -DCR_XCODE_VERSION=0800 -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -DCOMPONENT_BUILD -D__ASSERT_MACROS_DEFINE_VERSIONS_WITHOUT_UNDERSCORE=0 -D_DEBUG -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DWTF_USE_DYNAMIC_ANNOTATIONS=1 -DCONTENT_IMPLEMENTATION -DV8_USE_EXTERNAL_STARTUP_DATA -DLEVELDB_PLATFORM_CHROMIUM=1 -DSK_IGNORE_DW_GRAY_FIX -DSK_IGNORE_LINEONLY_AA_CONVEX_PATH_OPTS -DSKIA_DLL -DGR_GL_IGNORE_ES3_MSAA=0 -DSK_SUPPORT_GPU=1 -DSK_BUILD_FOR_MAC -DGOOGLE_PROTOBUF_NO_RTTI -DGOOGLE_PROTOBUF_NO_STATIC_INITIALIZER -DHAVE_PTHREAD -DPROTOBUF_USE_DLLS -DU_USING_ICU_NAMESPACE=0 -DU_ENABLE_DYLOAD=0 -DU_NOEXCEPT= -DICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_FILE -DMESA_EGL_NO_X11_HEADERS -DV8_SHARED -DUSING_V8_SHARED -DV8_SHARED -DUSING_V8_SHARED -DENABLE_WEBSOCKETS -DBORINGSSL_SHARED_LIBRARY -DFEATURE_ENABLE_SSL -DFEATURE_ENABLE_VOICEMAIL -DEXPAT_RELATIVE_PATH -DGTEST_RELATIVE_PATH -DNO_MAIN_THREAD_WRAPPING -DNO_SOUND_SYSTEM -DWEBRTC_CHROMIUM_BUILD -DWEBRTC_POSIX -DWEBRTC_MAC -DXML_STATIC -DSSL_USE_OPENSSL -DHAVE_OPENSSL_SSL_H -DFEATURE_ENABLE_SSL -DLOGGING=1 -DNO_MAIN_THREAD_WRAPPING -DFLAC__NO_DLL -I../.. -Igen -I../../third_party/khronos -I../../gpu -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/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/include/gpu -I../../third_party/skia/src/gpu -I../../third_party/protobuf/src -Igen/protoc_out -I../../third_party/protobuf/src -Igen/blink -I../../third_party/icu/source/common -I../../third_party/icu/source/i18n -I../../third_party/mesa/src/include -I../../third_party/WebKit -Igen/third_party/WebKit -I../../v8/include -Igen -I../../third_party/ced/src -I../../v8/include -I../../third_party/libwebm/source -I../../third_party/opus/src/include -I../../third_party/boringssl/src/include -I../../third_party/angle/src/common/third_party/numerics -Igen/angle -I../../third_party/libyuv -I../../third_party/libyuv/include -I../../third_party/re2/src -I../../third_party/zlib -Igen/ui/resources -Igen/ui/resources -Igen/content/browser/tracing -I../../third_party/webrtc_overrides -I../../testing/gtest/include -I../../third_party -I../../third_party/webrtc_overrides -I../../third_party -I../../third_party/expat/files/lib -I../../third_party/jsoncpp/overrides/include -I../../third_party/jsoncpp/source/include -fno-strict-aliasing -fstack-protector-strong -fcolor-diagnostics -arch x86_64 -Wall -Werror -Wextra -Wpartial-availability -Wno-missing-field-initializers -Wno-unused-parameter -Wno-c++11-narrowing -Wno-covered-switch-default -Wno-deprecated-register -Wno-unneeded-internal-declaration -Wno-inconsistent-missing-override -Wno-shift-negative-value -Wno-undefined-var-template -Wno-nonportable-include-path -O0 -gdwarf-2 -isysroot /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk -mmacosx-version-min=10.7 -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 check-templates -Xclang -plugin-arg-find-bad-constructs -Xclang follow-macro-expansion -Xclang -plugin-arg-find-bad-constructs -Xclang check-implicit-copy-ctors -Wheader-hygiene -Wstring-conversion -Wexit-time-destructors -Wno-unused-function -fno-threadsafe-statics -fvisibility-inlines-hidden -Wno-undefined-bool-conversion -Wno-tautological-undefined-compare -std=c++11 -stdlib=libc++ -fobjc-call-cxx-cdtors -Wobjc-missing-property-synthesis -fno-rtti -fno-exceptions -include obj/content/browser/browser/precompile.h-mm -c ../../content/browser/accessibility/browser_accessibility_cocoa.mm -o obj/content/browser/browser/browser_accessibility_cocoa.o
../../content/browser/accessibility/browser_accessibility_cocoa.mm:553:8: error: reference to 'NSAccessibilityRequiredAttribute' is ambiguous
      {NSAccessibilityRequiredAttribute, @"required"},
       ^
/Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk/System/Library/Frameworks/AppKit.framework/Headers/NSAccessibilityConstants.h:89:31: note: candidate found by name lookup is 'NSAccessibilityRequiredAttribute'
APPKIT_EXTERN NSString *const NSAccessibilityRequiredAttribute NS_AVAILABLE_MAC(10_12);  //(NSNumber *) - (boolValue) whether a form field is required to have content for successful submission of the form
                              ^
../../content/browser/accessibility/browser_accessibility_cocoa.mm:56:17: note: candidate found by name lookup is '(anonymous namespace)::NSAccessibilityRequiredAttribute'
NSString* const NSAccessibilityRequiredAttribute = @"AXRequired";


Please use labels and text to provide additional information.

I'll upload a CL for this.