Avoid ISE

      Bug: 5786209

Change-Id: I92321d8dfc2e2991a508e475d2353d5a6597156b
diff --git a/src/com/android/browser/PhoneUi.java b/src/com/android/browser/PhoneUi.java
index 1bc0f77..ee5ca40 100644
--- a/src/com/android/browser/PhoneUi.java
+++ b/src/com/android/browser/PhoneUi.java
@@ -428,7 +428,9 @@
             mAnimScreen = new AnimScreen(mActivity);
         }
         mAnimScreen.set(tab.getScreenshot());
-        mCustomViewContainer.addView(mAnimScreen.mMain, COVER_SCREEN_PARAMS);
+        if (mAnimScreen.mMain.getParent() == null) {
+            mCustomViewContainer.addView(mAnimScreen.mMain, COVER_SCREEN_PARAMS);
+        }
         mAnimScreen.mMain.layout(0, 0, mContentView.getWidth(),
                 mContentView.getHeight());
         mNavScreen.mScroller.finishScroller();