Support fade for remote images in React with nodes.

Summary:
Support fade for DrawImageWithPipeline so that images are faded in
when they are remotely fetched.

Differential Revision: D2804997

ReactAndroid/src/main/java/com/facebook/react/flat/AbstractDrawCommand.java

@@ -32,6 +32,7 @@ import android.graphics.Canvas;
 
   @Override
   public final void draw(FlatViewGroup parent, Canvas canvas) {
+    onPreDraw(parent, canvas);
     if (shouldClip()) {
       canvas.save();
       canvas.clipRect(mClipLeft, mClipTop, mClipRight, mClipBottom);
@@ -42,6 +43,9 @@ import android.graphics.Canvas;
     }
   }
 
+  protected void onPreDraw(FlatViewGroup parent, Canvas canvas) {
+  }
+
   /**
    * Updates boundaries of the AbstractDrawCommand and freezes it.
    * Will return a frozen copy if the current AbstractDrawCommand cannot be mutated.