Add SwapPromise support to LayerTreeHost and LayerTreeImpl

cc/base/swap_promise.h

Index: cc/base/swap_promise.h
diff --git a/cc/base/swap_promise.h b/cc/base/swap_promise.h
new file mode 100644
index 0000000000000000000000000000000000000000..69ffd5acf758b47faeeac740f7e1a101206723f5
--- /dev/null
+++ b/cc/base/swap_promise.h
@@ -0,0 +1,29 @@
+// Copyright 2013 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 CC_BASE_SWAP_PROMISE_H_
+#define CC_BASE_SWAP_PROMISE_H_
+
+#include <string>
+
+#include "base/callback.h"
+#include "base/callback_forward.h"
+
+namespace cc {
+
+struct SwapPromise {
+  SwapPromise(const base::Closure& did_swap_cb,
+              const base::Callback<void(const std::string&)>& swap_aborted_cb)
+      : did_swap_callback(did_swap_cb),
+        swap_aborted_callback(swap_aborted_cb) {}
+
+  ~SwapPromise() {}
+
+  base::Closure did_swap_callback;
+  base::Callback<void(const std::string&)> swap_aborted_callback;

[jamesr, 2013/11/12 03:15:04]

why does this take a std::string? from this patch it appears that only a small
set of strings could possibly be passed here, which would indicate that an enum
would be a better fit

[Yufeng Shen (Slow to review), 2013/11/13 21:05:04]

Done.

+};
+
+}  // namespace cc
+
+#endif  // CC_BASE_SWAP_PROMISE_H_