Make ChromeOS screenshots use async readback path

chrome/browser/ui/window_snapshot/window_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 CHROME_BROWSER_UI_WINDOW_SNAPSHOT_WINDOW_SNAPSHOT_H_
 #define CHROME_BROWSER_UI_WINDOW_SNAPSHOT_WINDOW_SNAPSHOT_H_
 
 #include <vector>
 
 #include "ui/gfx/native_widget_types.h"
+#include "ui/snapshot/snapshot.h"
 
 class PrefRegistrySimple;
 
 namespace gfx {
 class Rect;
 }
 
 namespace chrome {
 
 void RegisterScreenshotPrefs(PrefRegistrySimple* registry);
 
 // Grabs a snapshot of the rectangle area |snapshot_bounds| with respect to the
 // top left corner of the designated window and stores a PNG representation
 // into a byte vector. On Windows, |window| may be NULL to grab a snapshot of
 // the primary monitor. This takes into account calling user context (ie. checks
 // policy settings if taking screenshots is allowed), and is intended to be used
 // by browser code. If you need to take a screenshot for debugging purposes,
 // consider using ui::GrabWindowSnapshot.
 // Returns true if the operation is successful (ie. permitted).
-bool GrabWindowSnapshotForUser(
+bool GrabWindowSnapshotForUser(gfx::NativeWindow window,
+                               std::vector<unsigned char>* png_representation,
+                               const gfx::Rect& snapshot_bounds);
+
+void GrabWindowSnapshotForUserAsync(
     gfx::NativeWindow window,
-    std::vector<unsigned char>* png_representation,
-    const gfx::Rect& snapshot_bounds);
+    const gfx::Rect& snapshot_bounds,
+    scoped_refptr<base::TaskRunner> background_task_runner,
+    ui::GrabWindowSnapshotAsyncPNGCallback callback);
 
 }  // namespace chrome
 
 #endif  // CHROME_BROWSER_UI_WINDOW_SNAPSHOT_WINDOW_SNAPSHOT_H_