Multiple fixes to browser

- Ensure that clearing of the FLAG_DIM_BEHIND happens only once.
  Clearing FLAG_DIM_BEHIND window flag multiple time was causing
  unnecessary paint.
- Implement shouldDownloadFavicon API in Tab to optimize favicon
  download.

Change-Id: I8027565a29f2f1f6a2429a282c8727c6b4fe0d45
diff --git a/src/com/android/browser/Tab.java b/src/com/android/browser/Tab.java
index 789db54..3b57d9e 100644
--- a/src/com/android/browser/Tab.java
+++ b/src/com/android/browser/Tab.java
@@ -432,6 +432,11 @@
             }
         }
 
+        @Override
+        public boolean shouldDownloadFavicon(WebView view, String url) {
+            return true;
+        }
+
         /**
          * Updates the security state. This method is called when we discover
          * another resource to be loaded for this page (for example,