WIP: A couple of more ChannelMojo speedup ideas

ipc/mojo/async_handle_waiter.h

 // Copyright 2015 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 IPC_MOJO_ASYNC_HANDLE_WAITER_H_
 #define IPC_MOJO_ASYNC_HANDLE_WAITER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "ipc/ipc_export.h"
 #include "third_party/mojo/src/mojo/public/c/system/types.h"
 
 namespace IPC {
 namespace internal {
 
 // |AsyncHandleWaiter| waits on a mojo handle asynchronously and
 // invokes the given |callback| through |runner| when it is signaled.
 //  * To start waiting, the client must call |AsyncHandleWaiter::Wait()|.
 //    The client can call |Wait()| again once it is signaled and
 //    the |callback| is invoked.
 //  * To cancel waiting, delete the instance.
 //
 // |AsyncHandleWaiter| must be created, used and deleted only from the IO
 // |thread.
 class IPC_MOJO_EXPORT AsyncHandleWaiter {
  public:
   class Context;
 
-  explicit AsyncHandleWaiter(base::Callback<void(MojoResult)> callback);
+  class Delegate {
+   public:
+    virtual void PipeIsReady(MojoResult result) = 0;
+    virtual void MessageWasArrived(const void* bytes, uint32_t num_bytes) = 0;
+  };
+
+  explicit AsyncHandleWaiter(Delegate* delegate);
   ~AsyncHandleWaiter();
 
+  void SetMessageCallback(MojoHandle handle);
+  void ClearMessageCallback(MojoHandle handle);
   MojoResult Wait(MojoHandle handle, MojoHandleSignals signals);
 
  private:
   void InvokeCallback(MojoResult result);
+  void InvokeMessageCallback(const void* bytes, uint32_t num_bytes);
 
   scoped_refptr<Context> context_;
-  base::Callback<void(MojoResult)> callback_;
+  Delegate* delegate_;
+  base::Callback<void(MojoResult)> context_callback_;
+  base::Callback<bool(const void*, uint32_t)> context_message_callback_;
   base::WeakPtrFactory<AsyncHandleWaiter> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(AsyncHandleWaiter);
 };
 
 }  // namespace internal
 }  // namespace IPC
 
 #endif  // IPC_MOJO_ASYNC_HANDLE_WAITER_H_