Make WindowReachedScreen support async readback

ui/snapshot/snapshot_gtk.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/snapshot/snapshot.h"
 
 #include <gdk/gdkx.h>
 #include <gtk/gtk.h>
 
 #include "base/callback.h"
 #include "base/logging.h"
 #include "ui/base/x/x11_util.h"
+#include "ui/gfx/image/image.h"
 #include "ui/gfx/rect.h"
 
 namespace {
 
 cairo_status_t SnapshotCallback(void* closure,
                                 const unsigned char* data,
                                 unsigned int length) {
   std::vector<unsigned char>* png_representation =
       static_cast<std::vector<unsigned char>*>(closure);
 
@@ skipping 59 matching lines @@
   return GrabViewSnapshot(GTK_WIDGET(window_handle), png_representation,
       snapshot_bounds);
 }
 
 void GrabWindowSnapshotAndScaleAsync(
     gfx::NativeWindow window,
     const gfx::Rect& snapshot_bounds,
     const gfx::Size& target_size,
     scoped_refptr<base::TaskRunner> background_task_runner,
     GrabWindowSnapshotAsyncCallback callback) {
-  NOTIMPLEMENTED();
+  callback.Run(gfx::Image());
+}
+
+void GrabViewSnapshotAsync(
+    gfx::NativeView view,
+    const gfx::Rect& source_rect,
+    scoped_refptr<base::TaskRunner> background_task_runner,
+    const GrabWindowSnapshotAsyncPNGCallback& callback) {
+  callback.Run(scoped_refptr<base::RefCountedBytes>());
 }
 
 void GrabWindowSnapshotAsync(
     gfx::NativeWindow window,
     const gfx::Rect& source_rect,
     scoped_refptr<base::TaskRunner> background_task_runner,
     const GrabWindowSnapshotAsyncPNGCallback& callback) {
-  NOTIMPLEMENTED();
+  callback.Run(scoped_refptr<base::RefCountedBytes>());
 }
 
 }  // namespace ui