Make ui::Snapshot asynchronous on Android, remove CompositeAndReadback.

ui/snapshot/snapshot_async.h

Index: ui/snapshot/snapshot_async.h
diff --git a/ui/snapshot/snapshot_async.h b/ui/snapshot/snapshot_async.h
new file mode 100644
index 0000000000000000000000000000000000000000..41da62ba2ac0e07ace0e5caad10b433457e9f4e7
--- /dev/null
+++ b/ui/snapshot/snapshot_async.h
@@ -0,0 +1,42 @@
+// Copyright 2014 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_ASYNC_H_
+#define UI_SNAPSHOT_SNAPSHOT_ASYNC_H_
+
+#include "cc/output/copy_output_result.h"
+#include "ui/snapshot/snapshot.h"
+
+namespace base {
+class TaskRunner;
+}
+
+namespace gfx {
+class Size;
+}
+
+namespace ui {
+
+// Helper methods for async snapshots to convert a cc::CopyOutputResult into a
+// ui::GrabWindowSnapshot callback.
+class SnapshotAsync {
+ public:
+  static void ScaleCopyOutputResult(
+      const GrabWindowSnapshotAsyncCallback& callback,
+      const gfx::Size& target_size,
+      scoped_refptr<base::TaskRunner> background_task_runner,
+      scoped_ptr<cc::CopyOutputResult> result);
+
+  static void EncodeCopyOutputResult(
+      const GrabWindowSnapshotAsyncPNGCallback& callback,
+      scoped_refptr<base::TaskRunner> background_task_runner,
+      scoped_ptr<cc::CopyOutputResult> result);
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(SnapshotAsync);
+};
+
+}  // namespace ui
+
+#endif  // UI_SNAPSHOT_SNAPSHOT_ASYNC_H_