stop using hardware layers when workspace stops moving

helps workaround Bug 3417254

Change-Id: I874e5e52ab544fbb787e1021d6ee394e8f3a34d6

src/com/android/launcher2/Workspace.java

@@ -306,9 +306,14 @@ public class Workspace extends SmoothPagedView
                 }
                 mWallpaperOffset.setOverrideHorizontalCatchupConstant(false);
                 mAnimator = null;
+                enableChildrenLayers(false);
             }
         };
         mShrinkAnimationListener = new AnimatorListenerAdapter() {
+            @Override
+            public void onAnimationStart(Animator animation) {
+                enableChildrenLayers(true);
+            }
             @Override
             public void onAnimationEnd(Animator animation) {
                 mWallpaperOffset.setOverrideHorizontalCatchupConstant(false);
@@ -1253,6 +1258,25 @@ public class Workspace extends SmoothPagedView
         return super.onTouchEvent(ev);
     }
 
+    protected void enableChildrenLayers(boolean enable) {
+        for (int i = 0; i < getPageCount(); i++) {
+            setChildrenLayersEnabled(enable);
+        }
+    }
+    @Override
+    protected void pageBeginMoving() {
+        enableChildrenLayers(true);
+        super.pageBeginMoving();
+    }
+
+    @Override
+    protected void pageEndMoving() {
+        if (!mIsSmall && !mIsInUnshrinkAnimation) {
+            enableChildrenLayers(false);
+        }
+        super.pageEndMoving();
+    }
+
     @Override
     protected void onWallpaperTap(MotionEvent ev) {
         final int[] position = mTempCell;