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..5b213d2ddb73b78956840c34fa5b904e96b2f283
--- /dev/null
+++ b/cc/base/swap_promise.h
@@ -0,0 +1,51 @@
+// 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 "base/compiler_specific.h"
+
+namespace cc {
+
+// A SwapPromise can be queued into LTH/LTI to track if an expected swap

[danakj, 2013/11/13 23:22:09]

spell out LayerTreeHost(Impl) here

[Yufeng Shen (Slow to review), 2013/11/14 22:09:55]

Done.

+// buffer will happen or not. If the swap buffer happens, DidSwap() will

[danakj, 2013/11/13 23:22:09]

Can you reword this comment to match what I wrote in email about this? It's not
tracking a swap buffers so much as tracking that the current state of the tree
has been sent to the compositor's output.

[Yufeng Shen (Slow to review), 2013/11/14 22:09:55]

Done.

+// be called, and if the swap buffer somehow fails to happen, DidNotSwap()
+// will be called.
+// Client wishes to use SwapPromise should have a subclass that defines
+// the behavior of DidSwap() and DidNotSwap(). Notice that swap buffer can
+// fail at main/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:
+  enum SwapPromiseType {
+    SWAP_PROMISE_UNKNOWN,
+  };
+
+  explicit SwapPromise(SwapPromiseType type);
+  virtual ~SwapPromise() {}
+
+  enum DidNotSwapReason {
+    DID_NOT_SWAP_UNKNOWN,
+    SWAP_FAILS,
+    COMMIT_FAILS,
+    SWAP_PROMISE_LIST_OVERFLOW,
+  };
+
+  SwapPromiseType type() {

[danakj, 2013/11/13 23:22:09]

If there's only one type, what's the point of this?

[Yufeng Shen (Slow to review), 2013/11/14 22:09:55]

It is intended that subclass added in the future will add
more types here.

[danakj, 2013/11/20 03:00:55]

Then I prefer we add it in a later patch that will use it instead. That will
give appropriate context and no point in adding it here if it's not needed to
implement the SwapPromise system.

[Yufeng Shen (Slow to review), 2013/11/20 19:15:41]

removed.

+    return type_;
+  }
+
+  virtual void DidSwap() = 0;
+  virtual void DidNotSwap(DidNotSwapReason reason) = 0;
+
+ protected:
+  SwapPromiseType type_;
+};
+
+}  // namespace cc
+
+#endif  // CC_BASE_SWAP_PROMISE_H_