[mojo] Implement pipe fusion API

mojo/edk/system/message_pipe_dispatcher.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 MOJO_EDK_SYSTEM_MESSAGE_PIPE_DISPATCHER_H_
 #define MOJO_EDK_SYSTEM_MESSAGE_PIPE_DISPATCHER_H_
 
 #include <stdint.h>
 
 #include <queue>
@@ skipping 21 matching lines @@
   // state, and one can never return to a disconnected once connected.
   //
   // |pipe_id| is a unique identifier which can be used to track pipe endpoints
   // as they're passed around. |endpoint| is either 0 or 1 and again is only
   // used for tracking pipes (one side is always 0, the other is always 1.)
   MessagePipeDispatcher(NodeController* node_controller,
                         const ports::PortRef& port,
                         uint64_t pipe_id,
                         int endpoint);
 
+  // Fuses this pipe with |other|. Returns |true| on success or |false| on
+  // failure. Regardless of the return value, both dispatchers are closed by
+  // this call.
+  bool Fuse(MessagePipeDispatcher* other);
+
   // Dispatcher:
   Type GetType() const override;
   MojoResult Close() override;
   MojoResult Watch(MojoHandleSignals signals,
                    const Watcher::WatchCallback& callback,
                    uintptr_t context) override;
   MojoResult CancelWatch(uintptr_t context) override;
   MojoResult WriteMessage(const void* bytes,
                           uint32_t num_bytes,
                           const DispatcherInTransit* dispatchers,
@@ skipping 56 matching lines @@
   bool port_closed_ = false;
   AwakableList awakables_;
 
   DISALLOW_COPY_AND_ASSIGN(MessagePipeDispatcher);
 };
 
 }  // namespace edk
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_MESSAGE_PIPE_DISPATCHER_H_