Expose setting API to set ImageAnimationPolicy(Allowed, Once, None)

Source/platform/blink_platform.gypi

 {
   'includes': [
     'platform_generated.gypi',
   ],
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
@@ skipping 499 matching lines @@
       'graphics/GraphicsLayer.h',
       'graphics/GraphicsLayerClient.h',
       'graphics/GraphicsLayerDebugInfo.cpp',
       'graphics/GraphicsLayerDebugInfo.h',
       'graphics/GraphicsLayerFactory.h',
       'graphics/GraphicsTypes.cpp',
       'graphics/GraphicsTypes.h',
       'graphics/GraphicsTypes3D.h',
       'graphics/Image.cpp',
       'graphics/Image.h',
+      'graphics/ImageAnimationPolicy.h',
       'graphics/ImageBuffer.cpp',
       'graphics/ImageBuffer.h',
       'graphics/ImageBufferClient.h',
       'graphics/ImageBufferSurface.cpp',
       'graphics/ImageBufferSurface.h',
       'graphics/ImageDecodingStore.cpp',
       'graphics/ImageDecodingStore.h',
       'graphics/ImageFilter.cpp',
       'graphics/ImageFilter.h',
       'graphics/ImageFrameGenerator.cpp',
@@ skipping 434 matching lines @@
       'graphics/ImageFrameGeneratorTest.cpp',
       'graphics/ImageLayerChromiumTest.cpp',
       'graphics/test/MockImageDecoder.h',
       'graphics/test/MockWebGraphicsContext3D.h',
       'image-decoders/gif/GIFImageDecoderTest.cpp',
       'image-decoders/jpeg/JPEGImageDecoderTest.cpp',
       'image-decoders/webp/WEBPImageDecoderTest.cpp',
     ],
   },
 }