Make ChromeOS screenshots use async readback path

chrome/browser/ui/window_snapshot/window_snapshot.cc

Index: chrome/browser/ui/window_snapshot/window_snapshot.cc
diff --git a/chrome/browser/ui/window_snapshot/window_snapshot.cc b/chrome/browser/ui/window_snapshot/window_snapshot.cc
index 889d97d57c04d63c9bf23d1abff68334c6610b35..ab984778bf24df164b7a165673a88e62a9449e42 100644
--- a/chrome/browser/ui/window_snapshot/window_snapshot.cc
+++ b/chrome/browser/ui/window_snapshot/window_snapshot.cc
@@ -22,6 +22,17 @@ bool GrabWindowSnapshotForUser(
       snapshot_bounds);
 }
 
+void GrabWindowSnapshotForUserAsync(

[Jun Mukai, 2014/01/09 01:19:32]

I am not sure we need to declare this if the only user is ash/screenshot_taker.
Screenshot_taker already checks kDisableScreenshots, so you don't have to check
that again.

[enne (OOO), 2014/01/09 02:47:51]

That's a good point.  I'll remove this now and then come back and remove the
other sync version too once there's only caller in the future.

[enne (OOO), 2014/01/09 19:38:42]

Here's the followup to clean up window_snapshot once there's only one caller of
the sync version: https://codereview.chromium.org/132203004/

+    gfx::NativeWindow window,
+    const gfx::Rect& snapshot_bounds,
+    scoped_refptr<base::TaskRunner> background_task_runner,
+    ui::GrabWindowSnapshotAsyncPNGCallback callback) {
+  if (g_browser_process->local_state()->GetBoolean(prefs::kDisableScreenshots))
+    callback.Run(scoped_refptr<base::RefCountedBytes>());
+  ui::GrabWindowSnapshotAsync(
+      window, snapshot_bounds, background_task_runner, callback);
+}
+
 void RegisterScreenshotPrefs(PrefRegistrySimple* registry) {
   registry->RegisterBooleanPref(prefs::kDisableScreenshots, false);
 }