Bug 709817 - Ensure PZC is always accessed on the UI thread. r=pcwalton

Ensure that all public functions in PZC are always called from
the UI thread, so that internal variables are not mutated on
different threads. I also made animatedZoomTo private so that
it can't be inadvertently called from a non-UI thread outside
the class.

mobile/android/base/gfx/LayerController.java

@@ -281,8 +281,13 @@ public class LayerController {
 
     /** Aborts any pan/zoom animation that is currently in progress. */
     public void abortPanZoomAnimation() {
-        if (mPanZoomController != null)
-            mPanZoomController.abortAnimation();
+        if (mPanZoomController != null) {
+            mView.post(new Runnable() {
+                public void run() {
+                    mPanZoomController.abortAnimation();
+                }
+            });
+        }
     }
 
     /**