Revert "Revert "Clear the bitmap associated with canvases.""

This reverts commit 4e012846cd09caa85b018c36810e9a64adb87640.
diff --git a/src/com/android/launcher2/CachedTextView.java b/src/com/android/launcher2/CachedTextView.java
index ac2cc3b..f9f68a0 100644
--- a/src/com/android/launcher2/CachedTextView.java
+++ b/src/com/android/launcher2/CachedTextView.java
@@ -130,6 +130,7 @@
             setAlpha(prevAlpha);
             mIsBuildingCache = false;
             mCacheCanvas.restore();
+            mCacheCanvas.setBitmap(null);
 
             // A hack-- we set the text to be one space (we don't make it empty just to avoid any
             // potential issues with text measurement, like line height, etc.) so that the text view