Ensure calling mutate() on DrawableContainer creates a new state

Previously, a new state would only be created on newDrawable(), which
caused the first drawable loaded for a resource to share constant state
with the cached version. Even if mutate() was called, the constant
state was still shared and any changes were applied to the cached copy.

BUG: 18504919
Change-Id: I40d257867eb0a092ce580b9c4338ddc7406a031d

graphics/java/android/graphics/drawable/AnimationDrawable.java

@@ -342,12 +342,17 @@ public class AnimationDrawable extends DrawableContainer implements Runnable, An
     @Override
     public Drawable mutate() {
         if (!mMutated && super.mutate() == this) {
-            mAnimationState.mDurations = mAnimationState.mDurations.clone();
+            mAnimationState.mutate();
             mMutated = true;
         }
         return this;
     }
 
+    @Override
+    AnimationState cloneConstantState() {
+        return new AnimationState(mAnimationState, this, null);
+    }
+
     /**
      * @hide
      */
@@ -373,6 +378,10 @@ public class AnimationDrawable extends DrawableContainer implements Runnable, An
             }
         }
 
+        private void mutate() {
+            mDurations = mDurations.clone();
+        }
+
         @Override
         public Drawable newDrawable() {
             return new AnimationDrawable(this, null);