Fix RTL content jumping

Summary:
Whenever layout updates in a horizontal scrollview, in RTL mode we adjust the position - the impact *should* be that initially, we jump from position 0 to the right side of the scroll view,
such that scrolling starts from the right.

However, we were doing this entirely too aggressively before. We should only make this adjustment *if the layout changes the width*.

Changelog: [Android][Changed] Fixed jumpy RTL horizontal ScrollViews. If you have Android-specific JS hacks for handling RTL in ScrollViews, you probably can/probably want to remove them, because they should be reliable now and require fewer hacks.

Reviewed By: mdvacca

Differential Revision: D26771366

fbshipit-source-id: de11bd1cae1414018d88ce44b3583a8b15f3b330

Author: JoshuaGross

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

@@ -44,13 +44,6 @@ public void setRemoveClippedSubviews(boolean removeClippedSubviews) {
 
   @Override
   protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
-    /**
-     * Note: in RTL mode, *when layout width changes*, we adjust the scroll position. Practically,
-     * this means that on the first (meaningful) layout we will go from position 0 to position
-     * (right - screenWidth). In theory this means if the width of the view ever changes during
-     * layout again, scrolling could jump. Which shouldn't happen in theory, but... if you find a
-     * weird product bug that looks related, keep this in mind.
-     */
     if (mLayoutDirection == LAYOUT_DIRECTION_RTL) {
       // When the layout direction is RTL, we expect Yoga to give us a layout
       // that extends off the screen to the left so we re-center it with left=0
@@ -60,11 +53,20 @@ protected void onLayout(boolean changed, int left, int top, int right, int botto
       setLeft(newLeft);
       setRight(newRight);
 
-      // Call with the present values in order to re-layout if necessary
-      ReactHorizontalScrollView parent = (ReactHorizontalScrollView) getParent();
-      // Fix the ScrollX position when using RTL language
-      int offsetX = parent.getScrollX() + getWidth() - mCurrentWidth;
-      parent.reactScrollTo(offsetX, parent.getScrollY());
+      /**
+       * Note: in RTL mode, *when layout width changes*, we adjust the scroll position. Practically,
+       * this means that on the first (meaningful) layout we will go from position 0 to position
+       * (right - screenWidth). In theory this means if the width of the view ever changes during
+       * layout again, scrolling could jump. Which shouldn't happen in theory, but... if you find a
+       * weird product bug that looks related, keep this in mind.
+       */
+      if (mCurrentWidth != getWidth()) {
+        // Call with the present values in order to re-layout if necessary
+        ReactHorizontalScrollView parent = (ReactHorizontalScrollView) getParent();
+        // Fix the ScrollX position when using RTL language
+        int offsetX = parent.getScrollX() + getWidth() - mCurrentWidth;
+        parent.reactScrollTo(offsetX, parent.getScrollY());
+      }
     }
     mCurrentWidth = getWidth();
   }