Fix ReactHorizontalScrollView overflow issue

Summary: Fix ReactHorizontalScrollView so that its children won't overflow. (Task: https://our.intern.facebook.com/intern/tasks/?t=31128239)

Reviewed By: achen1

Differential Revision: D8923947

fbshipit-source-id: 56c36b25c29a87a306d92544273603d0d086edc0

Author: Jiaqi Wu

ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.java

@@ -38,6 +38,7 @@ public class ReactHorizontalScrollView extends HorizontalScrollView implements
 
   private final OnScrollDispatchHelper mOnScrollDispatchHelper = new OnScrollDispatchHelper();
   private final VelocityHelper mVelocityHelper = new VelocityHelper();
+  private final Rect mRect = new Rect();
 
   private boolean mActivelyScrolling;
   private @Nullable Rect mClippingRect;
@@ -102,6 +103,13 @@ public void flashScrollIndicators() {
     awakenScrollBars();
   }
 
+  @Override
+  protected void onDraw(Canvas canvas) {
+    getDrawingRect(mRect);
+    canvas.clipRect(mRect);
+    super.onDraw(canvas);
+  }
+
   @Override
   protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
     MeasureSpecAssertions.assertExplicitMeasureSpec(widthMeasureSpec, heightMeasureSpec);