Fix flash when switching from app window to snapshot.

- If there is any delay in launcher draw, then we will finish the
  transition and hide the app window before launcher has had a chance to
  draw the task view with the updated snapshot.

Change-Id: I81c5b467f32520fd7474bde0e89819336292e84f

src/com/android/launcher3/util/ViewOnDrawExecutor.java

@@ -49,9 +49,16 @@ public class ViewOnDrawExecutor implements Executor, OnDrawListener, Runnable,
     }
 
     public void attachTo(Launcher launcher) {
+        attachTo(launcher, launcher.getWorkspace(), true /* waitForLoadAnimation */);
+    }
+
+    public void attachTo(Launcher launcher, View attachedView, boolean waitForLoadAnimation) {
         mLauncher = launcher;
-        mAttachedView = launcher.getWorkspace();
+        mAttachedView = attachedView;
         mAttachedView.addOnAttachStateChangeListener(this);
+        if (!waitForLoadAnimation) {
+            mLoadAnimationCompleted = true;
+        }
 
         attachObserver();
     }
@@ -74,7 +81,7 @@ public class ViewOnDrawExecutor implements Executor, OnDrawListener, Runnable,
     }
 
     @Override
-    public void onViewDetachedFromWindow(View v) { }
+    public void onViewDetachedFromWindow(View v) {}
 
     @Override
     public void onDraw() {
@@ -101,10 +108,7 @@ public class ViewOnDrawExecutor implements Executor, OnDrawListener, Runnable,
         // Post the pending tasks after both onDraw and onLoadAnimationCompleted have been called.
         if (mLoadAnimationCompleted && mFirstDrawCompleted && !mCompleted) {
             mIsExecuting = true;
-            for (final Runnable r : mTasks) {
-                mExecutor.execute(r);
-            }
-            markCompleted();
+            runAllTasks();
         }
     }
 
@@ -121,4 +125,15 @@ public class ViewOnDrawExecutor implements Executor, OnDrawListener, Runnable,
         }
         LauncherModel.setWorkerPriority(Process.THREAD_PRIORITY_DEFAULT);
     }
+
+    protected boolean isCompleted() {
+        return mCompleted;
+    }
+
+    protected void runAllTasks() {
+        for (final Runnable r : mTasks) {
+            mExecutor.execute(r);
+        }
+        markCompleted();
+    }
 }