Make ChromeOS screenshots use async readback path

ui/snapshot/snapshot.h

 // 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.
 
 #ifndef UI_SNAPSHOT_SNAPSHOT_H_
 #define UI_SNAPSHOT_SNAPSHOT_H_
 
 #include <vector>
 
 #include "base/callback_forward.h"
 #include "base/memory/ref_counted.h"
+#include "base/memory/ref_counted_memory.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/snapshot/snapshot_export.h"
 
 namespace base {
 class TaskRunner;
 }
 
 namespace gfx {
 class Rect;
 class Image;
@@ skipping 20 matching lines @@
 typedef base::Callback<void(const gfx::Image& snapshot)>
     GrabWindowSnapshotAsyncCallback;
 // GrabWindowSnapshotAndScaleAsync() copies snapshot of |source_rect| from
 // window and scales it to |target_size| asynchronously.
 SNAPSHOT_EXPORT void GrabWindowSnapshotAndScaleAsync(
     gfx::NativeWindow window,
     const gfx::Rect& source_rect,
     const gfx::Size& target_size,
     scoped_refptr<base::TaskRunner> background_task_runner,
     const GrabWindowSnapshotAsyncCallback& callback);
+
+typedef base::Callback<void(scoped_refptr<base::RefCountedBytes> png_data)>
+    GrabWindowSnapshotAsyncPNGCallback;
 SNAPSHOT_EXPORT void GrabWindowSnapshotAsync(
     gfx::NativeWindow window,
     const gfx::Rect& source_rect,
     scoped_refptr<base::TaskRunner> background_task_runner,
-    const GrabWindowSnapshotAsyncCallback& callback);
+    const GrabWindowSnapshotAsyncPNGCallback& callback);
 
 }  // namespace ui
 
 #endif  // UI_SNAPSHOT_SNAPSHOT_H_