Blink Support for Overlay Scrollbar Animation

Source/web/web.gypi

 {
   'variables': {
     'web_files': [
       'AssertMatchingEnums.cpp',
       'AssociatedURLLoader.cpp',
       'AssociatedURLLoader.h',
       'BackForwardClientImpl.cpp',
       'BackForwardClientImpl.h',
       'ChromeClientImpl.cpp',
       'ChromeClientImpl.h',
@@ skipping 315 matching lines @@
           'web_unittest_files': [
             'tests/LocaleMacTest.cpp',
           ],
         }
       ],
       ['OS!="mac"',
         {
           'web_unittest_files': [
             # Mac uses ScrollAnimatorMac instead of ScrollAnimatorNone.
             'tests/ScrollAnimatorNoneTest.cpp',
+            'tests/ScrollbarStateTransitionAnimatorTest.cpp',
           ],
         }
       ],
       ['os_posix==1 and OS!="mac"',
         {
           'web_unittest_files': [
             'tests/LocaleICUTest.cpp',
           ],
         }
       ],
     ],
   },
 }