Infrastructure for supporting wallpaper previews.

Various things that will allow us to show previews of wallpapers.
Also some fixes to animations across wallpapers.
diff --git a/core/java/android/app/Activity.java b/core/java/android/app/Activity.java
index 10e6299..80d7285 100644
--- a/core/java/android/app/Activity.java
+++ b/core/java/android/app/Activity.java
@@ -1930,11 +1930,32 @@
      * 
      * @see #hasWindowFocus()
      * @see #onResume
+     * @see View#onWindowFocusChanged(boolean)
      */
     public void onWindowFocusChanged(boolean hasFocus) {
     }
     
     /**
+     * Called when the main window associated with the activity has been
+     * attached to the window manager.
+     * See {@link View#onAttachedToWindow() View.onAttachedToWindow()}
+     * for more information.
+     * @see View#onAttachedToWindow
+     */
+    public void onAttachedToWindow() {
+    }
+    
+    /**
+     * Called when the main window associated with the activity has been
+     * detached from the window manager.
+     * See {@link View#onDetachedFromWindow() View.onDetachedFromWindow()}
+     * for more information.
+     * @see View#onDetachedFromWindow
+     */
+    public void onDetachedFromWindow() {
+    }
+    
+    /**
      * Returns true if this activity's <em>main</em> window currently has window focus.
      * Note that this is not the same as the view itself having focus.
      *