Clear the bitmap from the canvas in a lot of places.

Change-Id: I6b2071ac7b348c473b9bdd1b972d095aebbb4fb3
diff --git a/core/java/android/app/ActivityThread.java b/core/java/android/app/ActivityThread.java
index 8931675..c566104 100644
--- a/core/java/android/app/ActivityThread.java
+++ b/core/java/android/app/ActivityThread.java
@@ -2503,6 +2503,7 @@
                     mAvailThumbnailBitmap = thumbnail;
                     thumbnail = null;
                 }
+                cv.setBitmap(null);
             }
 
         } catch (Exception e) {