Implement CSSOM Smooth Scroll API

Source/platform/blink_platform.gypi

 {
   'includes': [
     'platform_generated.gypi',
   ],
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
@@ skipping 730 matching lines @@
       'network/WebSocketHandshakeRequest.h',
       'network/WebSocketHandshakeResponse.cpp',
       'network/WebSocketHandshakeResponse.h',
       'plugins/PluginData.cpp',
       'plugins/PluginData.h',
       'plugins/PluginListBuilder.cpp',
       'plugins/PluginListBuilder.h',
       'scroll/FramelessScrollView.cpp',
       'scroll/FramelessScrollView.h',
       'scroll/FramelessScrollViewClient.h',
+      'scroll/ProgrammaticScrollAnimator.cpp',
+      'scroll/ProgrammaticScrollAnimator.h',
       'scroll/ScrollAnimator.cpp',
       'scroll/ScrollAnimator.h',
       'scroll/ScrollAnimatorNone.cpp',
       'scroll/ScrollAnimatorNone.h',
       'scroll/ScrollTypes.h',
       'scroll/ScrollView.cpp',
       'scroll/ScrollableArea.cpp',
       'scroll/ScrollableArea.h',
       'scroll/Scrollbar.cpp',
       'scroll/Scrollbar.h',
@@ skipping 189 matching lines @@
       'graphics/ImageLayerChromiumTest.cpp',
       'graphics/OpaqueRectTrackingContentLayerDelegateTest.cpp',
       'graphics/test/MockImageDecoder.h',
       'graphics/test/MockWebGraphicsContext3D.h',
       'image-decoders/gif/GIFImageDecoderTest.cpp',
       'image-decoders/jpeg/JPEGImageDecoderTest.cpp',
       'image-decoders/webp/WEBPImageDecoderTest.cpp',
     ],
   },
 }