Refactor Scroll Customization to share cc::ScrollStateData with blink.

third_party/WebKit/Source/platform/blink_platform.gypi

 {
   'includes': [
     'platform_generated.gypi',
   ],
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.h',
       'CheckedInt.h',
       'ContentDecryptionModuleResult.h',
@@ skipping 871 matching lines @@
       'scroll/ScrollbarThemeMacNonOverlayAPI.mm',
       'scroll/ScrollbarThemeMacOverlayAPI.h',
       'scroll/ScrollbarThemeMacOverlayAPI.mm',
       'scroll/ScrollbarThemeMock.cpp',
       'scroll/ScrollbarThemeMock.h',
       'scroll/ScrollbarThemeNonMacCommon.cpp',
       'scroll/ScrollbarThemeNonMacCommon.h',
       'scroll/ScrollbarThemeOverlay.cpp',
       'scroll/ScrollbarThemeOverlay.h',
       'scroll/ScrollbarThemeOverlayMock.h',
+      'scroll/ScrollStateData.h',
       'speech/PlatformSpeechSynthesisUtterance.cpp',
       'speech/PlatformSpeechSynthesisUtterance.h',
       'speech/PlatformSpeechSynthesisVoice.cpp',
       'speech/PlatformSpeechSynthesisVoice.h',
       'speech/PlatformSpeechSynthesizer.cpp',
       'speech/PlatformSpeechSynthesizer.h',
       'text/BidiCharacterRun.cpp',
       'text/BidiCharacterRun.h',
       'text/BidiContext.cpp',
       'text/BidiContext.h',
@@ skipping 247 matching lines @@
       ['OS!="mac"',
         {
           'platform_test_files': [
             'scroll/ScrollAnimatorTest.cpp',
           ],
         }
       ],
     ],
   },
 }