Trace main thread commit in flow events.

cc/output/swap_promise.h

 // 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_OUTPUT_SWAP_PROMISE_H_
 #define CC_OUTPUT_SWAP_PROMISE_H_
 
 #include "cc/output/compositor_frame_metadata.h"
 
 namespace cc {
@@ skipping 21 matching lines @@
 //   DidActivate() ; DidNotSwap()
 //
 // Clients that wish to use SwapPromise should have a subclass that defines
 // the behavior of DidActivate(), 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 Did*() methods 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 Did*().
+//

[Yufeng Shen (Slow to review), 2015/06/16 17:54:16]

extra line

 class CC_EXPORT SwapPromise {
  public:
   enum DidNotSwapReason {
     SWAP_FAILS,
     COMMIT_FAILS,
     COMMIT_NO_UPDATE,
     ACTIVATION_FAILS,
   };
 
   SwapPromise() {}
   virtual ~SwapPromise() {}
 
   virtual void DidActivate() = 0;
   virtual void DidSwap(CompositorFrameMetadata* metadata) = 0;
   virtual void DidNotSwap(DidNotSwapReason reason) = 0;
+  // OnCommit is only called for LatencyInfoSwapPromise
+  virtual void OnCommit() {}

[Yufeng Shen (Slow to review), 2015/06/16 17:54:16]

Should not mention subclass's behavior, only mention under what conditionis this
callback triggered, e,g,

"This is called when main thread starts commit."

 
   // A non-zero trace id identifies a trace flow object that is embedded in the
   // swap promise. This can be used for registering additional flow steps to
   // visualize the object's path through the system.
   virtual int64 TraceId() const = 0;
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_SWAP_PROMISE_H_