Convert Settings::rootLayerScrolls to RuntimeEnabledFeatures

third_party/WebKit/Source/platform/blink_platform.gypi

 {
   'includes': [
     'platform_generated.gypi',
   ],
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.h',
       'CheckedInt.h',
       'ContentDecryptionModuleResult.h',
@@ skipping 1387 matching lines @@
       'testing/GeometryPrinters.cpp',
       'testing/GeometryPrinters.h',
       'testing/HistogramTester.cpp',
       'testing/HistogramTester.h',
       'testing/MessageLoopForMojo.h',
       'testing/PaintPrinters.cpp',
       'testing/PaintPrinters.h',
       'testing/PictureMatchers.cpp',
       'testing/PictureMatchers.h',
       'testing/PlatformTestPrinters.cpp',
+      'testing/RuntimeEnabledFeaturesTestHelpers.h',
       'testing/TestingPlatformSupport.cpp',
       'testing/TestingPlatformSupport.h',
       'testing/TestPaintArtifact.cpp',
       'testing/TestPaintArtifact.h',
       'testing/TransformPrinters.cpp',
       'testing/TransformPrinters.h',
       'testing/URLTestHelpers.cpp',
       'testing/URLTestHelpers.h',
       'testing/UnitTestHelpers.cpp',
       'testing/UnitTestHelpers.h',
@@ skipping 36 matching lines @@
       ['use_default_render_theme==1',
         {
           'platform_test_files': [
             'scroll/ScrollbarThemeAuraTest.cpp',
           ],
         }
       ],
     ],
   },
 }