Do less work in Nodes when clipping isn't needed

Summary:
By default, Nodes causes views to not be clipped, unless overflow is
explicitly set to hidden. Consequently, Nodes sets all the clipping bounds to
negative infinity, and does some extra work (saving the canvas layer,
clipping, etc) before drawing. This optimization skips the extra work when
it's not needed.

Reviewed By: sriramramani

Differential Revision: D3161268

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

@@ -21,9 +21,13 @@ import android.graphics.Canvas;
 
   @Override
   public void draw(FlatViewGroup parent, Canvas canvas) {
-    canvas.save();
-    applyClipping(canvas);
-    parent.drawNextChild(canvas);
-    canvas.restore();
+    if (mNeedsClipping) {
+      canvas.save();
+      applyClipping(canvas);
+      parent.drawNextChild(canvas);
+      canvas.restore();
+    } else {
+      parent.drawNextChild(canvas);
+    }
   }
 }