Do not allow javascript to change window focus.

Bug: 2161671
diff --git a/src/com/android/browser/Tab.java b/src/com/android/browser/Tab.java
index 3bb136c..447e6be 100644
--- a/src/com/android/browser/Tab.java
+++ b/src/com/android/browser/Tab.java
@@ -660,14 +660,6 @@
         }
 
         @Override
-        public void onRequestFocus(WebView view) {
-            if (!mInForeground) {
-                mActivity.switchToTab(mActivity.getTabControl().getTabIndex(
-                        Tab.this));
-            }
-        }
-
-        @Override
         public void onCloseWindow(WebView window) {
             if (mParentTab != null) {
                 // JavaScript can only close popup window.