Unload widget previews when launcher is not visible

Can save ~1-2MB of RAM

Bug #5104303

Change-Id: I992bec33052f4d2c201e528b5edf384d05960e71
diff --git a/src/com/android/launcher2/PagedView.java b/src/com/android/launcher2/PagedView.java
index ba303a1..3f5652e 100644
--- a/src/com/android/launcher2/PagedView.java
+++ b/src/com/android/launcher2/PagedView.java
@@ -143,7 +143,7 @@
 
     private PageSwitchListener mPageSwitchListener;
 
-    private ArrayList<Boolean> mDirtyPageContent;
+    protected ArrayList<Boolean> mDirtyPageContent;
 
     // choice modes
     protected static final int CHOICE_MODE_NONE = 0;