Change the shadow when view changes

Currently shadow is only listening to scrolling behavior for
ScrollingView, but didn't handled the view changes. This fix will update
the shadow view visibility #onGlobalLayout.

Bug: 1127816
Change-Id: I3a0b04bfb077d543fa0b41a9ece7890e5198d77f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2416565
Commit-Queue: Wenyu Fu <wenyufu@chromium.org>
Reviewed-by: Theresa  <twellington@chromium.org>
Reviewed-by: Sky Malice <skym@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808414}

chrome/android/java/src/org/chromium/chrome/browser/firstrun/TosAndUmaFragmentView.java

@@ -76,7 +76,10 @@ public class TosAndUmaFragmentView extends FrameLayout {
         mShadow = findViewById(R.id.shadow);
 
         // Set up shadow.
+        // Needed when scrolling to/away from the bottom of the ScrollView.
         mScrollView.getViewTreeObserver().addOnScrollChangedListener(this::updateShadowVisibility);
+        // Needed when other elements are added / removed from ScrollView.
+        mScrollView.getViewTreeObserver().addOnGlobalLayoutListener(this::updateShadowVisibility);
 
         // Cache resource dimensions that used in #onMeasure.
         mImageBottomMargin = getResources().getDimensionPixelSize(R.dimen.fre_image_bottom_margin);