Add deprecation message for -webkit-background-composite

third_party/WebKit/Source/core/core.gypi

 {
     'includes': [
         'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/KeyframeEffect.idl',
             'animation/EffectModel.idl',
             'animation/AnimationEffectReadOnly.idl',
@@ skipping 1594 matching lines @@
             'frame/DOMWindowEventHandlers.h',
             'frame/DOMWindowLifecycleNotifier.cpp',
             'frame/DOMWindowLifecycleNotifier.h',
             'frame/DOMWindowLifecycleObserver.h',
             'frame/DOMWindowProperty.cpp',
             'frame/DOMWindowProperty.h',
             'frame/DOMWindowTimers.cpp',
             'frame/DOMWindowTimers.h',
             'frame/DeprecatedScheduleStyleRecalcDuringLayout.cpp',
             'frame/DeprecatedScheduleStyleRecalcDuringLayout.h',
+            'frame/DeprecationHelper.cpp',
+            'frame/DeprecationHelper.h',
             'frame/DeviceSingleWindowEventController.cpp',
             'frame/DeviceSingleWindowEventController.h',
             'frame/EventHandlerRegistry.cpp',
             'frame/EventHandlerRegistry.h',
             'frame/Frame.cpp',
             'frame/Frame.h',
             'frame/FrameConsole.cpp',
             'frame/FrameHost.cpp',
             'frame/FrameHost.h',
             'frame/FrameOwner.h',
@@ skipping 2404 matching lines @@
             'style/SVGComputedStyleTest.cpp',
             'svg/SVGPathParserTest.cpp',
             'svg/UnsafeSVGAttributeSanitizationTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'timing/MemoryInfoTest.cpp',
             'workers/WorkerThreadTest.cpp',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }