Implement autoplay gesture override experiment.

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 2585 matching lines @@
             'events/WindowEventContext.cpp',
             'events/WindowEventContext.h',
             'input/EventHandler.cpp',
             'input/EventHandler.h',
             'input/InputDeviceCapabilities.cpp',
             'input/InputDeviceCapabilities.h',
             'input/TouchActionUtil.cpp',
             'input/TouchActionUtil.h',
         ],
         'webcore_html_files': [
+            'html/AutoplayExperimentConfig.cpp',
+            'html/AutoplayExperimentConfig.h',
+            'html/AutoplayExperimentHelper.cpp',
+            'html/AutoplayExperimentHelper.h',
             'html/ClassList.cpp',
             'html/ClassList.h',
             'html/CrossOriginAttribute.cpp',
             'html/CrossOriginAttribute.h',
             'html/DocumentNameCollection.cpp',
             'html/DocumentNameCollection.h',
             'html/FormAssociatedElement.cpp',
             'html/FormData.cpp',
             'html/FormData.h',
             'html/HTMLAllCollection.cpp',
@@ skipping 1250 matching lines @@
             'style/OutlineValueTest.cpp',
             'style/SVGComputedStyleTest.cpp',
             'svg/UnsafeSVGAttributeSanitizationTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'timing/MemoryInfoTest.cpp',
             'workers/WorkerThreadTest.cpp',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }