Clear bitmap from canvas after done drawing to it.

Change-Id: I0ebc8510021a2dd0b147ced7890d939ec47809f6
diff --git a/src/com/android/browser/TabBar.java b/src/com/android/browser/TabBar.java
index 2b4dd63..d1652dd 100644
--- a/src/com/android/browser/TabBar.java
+++ b/src/com/android/browser/TabBar.java
@@ -243,6 +243,7 @@
         Canvas c = new Canvas(b);
         drawable.setBounds(0, 0, width, height);
         drawable.draw(c);
+        c.setBitmap(null);
         return b;
     }