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diff --git a/cc/base/swap_promise.h b/cc/base/swap_promise.h
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+// 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_
+
+namespace cc {
+
+const unsigned int kMaxQueuedSwapPromiseNumber = 100;
+
+// When a change to the compositor's state/invalidation/whatever happens, a
+// Swap Promise can be inserted into LayerTreeHost/LayerTreeImpl, to track
+// whether the compositor's reply to the new state/invaliadtion/whatever is
+// completed in the compositor, i.e. the compositor knows it has been sent
+// to its output or not.
+//
+// If the new compositor state is sent to the output, SwapPromise::DidSwap()
+// will be called, and if the compositor fails to send its new state to the
+// output, SwapPromise::DidNotSwap() will be called.
+//
+// Client wishes to use SwapPromise should have a subclass that defines
+// the behavior of DidSwap() and DidNotSwap(). Notice that the promise can
+// be broken at either main or impl thread, e.g. commit fails on main thread,
+// new frame data has no actual damage so LayerTreeHostImpl::SwapBuffers()
+// bails out early on impl thread, so don't assume that DidSwap() and
+// DidNotSwap() are called at a particular thread. It is better to let the
+// subclass carry thread-safe member data and operate on that member data in
+// DidSwap() and DidNotSwap().
+class SwapPromise {
+ public:
+  SwapPromise() {}
+  virtual ~SwapPromise() {}
+
+  enum DidNotSwapReason {
+    DID_NOT_SWAP_UNKNOWN,
+    SWAP_FAILS,
+    COMMIT_FAILS,
+    SWAP_PROMISE_LIST_OVERFLOW,
+  };
+
+  virtual void DidSwap() = 0;
+  virtual void DidNotSwap(DidNotSwapReason reason) = 0;
+};
+
+}  // namespace cc
+
+#endif  // CC_BASE_SWAP_PROMISE_H_