Implements getImageAnimationPolicy() at ImageLoader.

Source/platform/graphics/ImageAnimationPolicy.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ImageAnimationPolicy_h
 #define ImageAnimationPolicy_h
 
 namespace blink {
 
 // ImageAnimationPolicy is used for controlling image animation
 // when image frame is rendered for animation
 
 enum ImageAnimationPolicy {
     // Animate the image (the default).
     ImageAnimationPolicyAllowed,
     // Animate image just once.
     ImageAnimationPolicyAnimateOnce,
     // Show the first frame and do not animate.
-    ImageAnimationPolicyNoAnimation
+    ImageAnimationPolicyNoAnimation,
+    // Need to update policy
+    ImageAnimationPolicyInvalid
 };
 
 } // namespace blink
 
 #endif // ImageAnimationPolicy_h