[mojo] Implement pipe fusion API

mojo/edk/system/message_pipe_dispatcher.cc

 // 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.
 
 #include "mojo/edk/system/message_pipe_dispatcher.h"
 
 #include <limits>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
@@ skipping 81 matching lines @@
       pipe_id_(pipe_id),
       endpoint_(endpoint) {
   DVLOG(2) << "Creating new MessagePipeDispatcher for port " << port.name()
            << " [pipe_id=" << pipe_id << "; endpoint=" << endpoint << "]";
 
   node_controller_->SetPortObserver(
       port_,
       make_scoped_refptr(new PortObserverThunk(this)));
 }
 
+bool MessagePipeDispatcher::Fuse(MessagePipeDispatcher* other) {
+  node_controller_->SetPortObserver(port_, nullptr);
+  node_controller_->SetPortObserver(other->port_, nullptr);
+
+  ports::PortRef port0;
+  {
+    base::AutoLock lock(signal_lock_);
+    port0 = port_;
+    port_closed_ = true;
+    awakables_.CancelAll();
+  }
+
+  ports::PortRef port1;
+  {
+    base::AutoLock lock(other->signal_lock_);
+    port1 = other->port_;
+    other->port_closed_ = true;
+    other->awakables_.CancelAll();
+  }
+
+  // Both ports are always closed by this call.
+  int rv = node_controller_->MergeLocalPorts(port0, port1);
+  return rv == ports::OK;
+}
+
 Dispatcher::Type MessagePipeDispatcher::GetType() const {
   return Type::MESSAGE_PIPE;
 }
 
 MojoResult MessagePipeDispatcher::Close() {
   base::AutoLock lock(signal_lock_);
   DVLOG(1) << "Closing message pipe " << pipe_id_ << " endpoint " << endpoint_
            << " [port=" << port_.name() << "]";
   return CloseNoLock();
 }
@@ skipping 531 matching lines @@
     DVLOG(1) << "Peer closure detected on message pipe " << pipe_id_
              << " endpoint " << endpoint_ << " [port=" << port_.name() << "]";
   }
 #endif
 
   awakables_.AwakeForStateChange(GetHandleSignalsStateNoLock());
 }
 
 }  // namespace edk
 }  // namespace mojo