Deferring wallpaper update to improve workspace scrolling (issue 5506959)

-> On the Xoom, this change gets us back up to 60 fps. The
   change is really more of a workaround for the fact that we don't
   have vsync, and we ought to be able to change it back once we do.

Change-Id: I80888f18887bf5f2fed72c19641ed430ef6dbfcf

Author: Adam Cohen

core/java/android/app/WallpaperManager.java

@@ -212,7 +212,11 @@ public void onWallpaperChanged() {
              */
             mHandler.sendEmptyMessage(MSG_CLEAR_WALLPAPER);
         }
-        
+
+        public Handler getHandler() {
+            return mHandler;
+        }
+
         public Bitmap peekWallpaperBitmap(Context context, boolean returnDefault) {
             synchronized (this) {
                 if (mWallpaper != null) {
@@ -604,7 +608,7 @@ public void suggestDesiredDimensions(int minimumWidth, int minimumHeight) {
             // Ignore
         }
     }
-    
+
     /**
      * Set the position of the current wallpaper within any larger space, when
      * that wallpaper is visible behind the given window.  The X and Y offsets
@@ -619,16 +623,23 @@ public void suggestDesiredDimensions(int minimumWidth, int minimumHeight) {
      * @param yOffset The offset along the Y dimension, from 0 to 1.
      */
     public void setWallpaperOffsets(IBinder windowToken, float xOffset, float yOffset) {
-        try {
-            //Log.v(TAG, "Sending new wallpaper offsets from app...");
-            ViewRootImpl.getWindowSession(mContext.getMainLooper()).setWallpaperPosition(
-                    windowToken, xOffset, yOffset, mWallpaperXStep, mWallpaperYStep);
-            //Log.v(TAG, "...app returning after sending offsets!");
-        } catch (RemoteException e) {
-            // Ignore.
-        }
+        final IBinder fWindowToken = windowToken;
+        final float fXOffset = xOffset;
+        final float fYOffset = yOffset;
+        sGlobals.getHandler().post(new Runnable() {
+            public void run() {
+                try {
+                    //Log.v(TAG, "Sending new wallpaper offsets from app...");
+                    ViewRootImpl.getWindowSession(mContext.getMainLooper()).setWallpaperPosition(
+                            fWindowToken, fXOffset, fYOffset, mWallpaperXStep, mWallpaperYStep);
+                    //Log.v(TAG, "...app returning after sending offsets!");
+                } catch (RemoteException e) {
+                    // Ignore.
+                }
+            }
+        });
     }
-    
+
     /**
      * For applications that use multiple virtual screens showing a wallpaper,
      * specify the step size between virtual screens. For example, if the