Don't render while pinching. Reduces jank and makes zooming easier to debug.

mobile/android/base/gfx/GeckoLayerClient.java

@@ -265,10 +265,8 @@ public abstract class GeckoLayerClient extends LayerClient implements GeckoEvent
     }
 
     private void adjustViewportWithThrottling() {
-        // FIXME: Allow redraw while a finger is down, but only if we're about to checkerboard.
-        // This requires fixing aboutToCheckerboard() to know about the new buffer size.
-        /*if (!getLayerController().getRedrawHint())
-            return;*/
+        if (!getLayerController().getRedrawHint())
+            return;
 
         if (mPendingViewportAdjust)
             return;

mobile/android/base/gfx/LayerController.java

@@ -319,12 +319,15 @@ public class LayerController {
      * would prefer that the action didn't take place.
      */
     public boolean getRedrawHint() {
+        // FIXME: Allow redraw while a finger is down, but only if we're about to checkerboard.
+        // This requires fixing aboutToCheckerboard() to know about the new buffer size.
+
         if (mForceRedraw) {
             mForceRedraw = false;
             return true;
         }
 
-        return aboutToCheckerboard() && mPanZoomController.getRedrawHint();
+        return mPanZoomController.getRedrawHint();
     }
 
     private RectF getTileRect() {

mobile/android/base/ui/PanZoomController.java

@@ -819,7 +819,7 @@ public class PanZoomController
     }
 
     public boolean getRedrawHint() {
-        return (mState == PanZoomState.NOTHING || mState == PanZoomState.FLING);
+        return (mState != PanZoomState.PINCHING && mState != PanZoomState.ANIMATED_ZOOM);
     }
 
     private void sendPointToGecko(String event, MotionEvent motionEvent) {