[Thread Safety] Replace WebString bound by cross-thread base::Bind() with base::string16

content/child/navigator_connect/service_port_provider.cc

 // Copyright 2014 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 "content/child/navigator_connect/service_port_provider.h"
 
 #include "base/lazy_instance.h"
 #include "base/single_thread_task_runner.h"
 #include "base/task_runner_util.h"
 #include "content/child/child_thread_impl.h"
@@ skipping 53 matching lines @@
   // to make sure all ports have been fully initialized. Actually sending the
   // message can safely be done on this thread, and using mojo, since there
   // shouldn't be any other IPCs where ordering matters.
   scoped_ptr<blink::WebMessagePortChannelArray> channel_array(channels);
   base::PostTaskAndReplyWithResult(
       main_loop_.get(), FROM_HERE,
       base::Bind(
           &WebMessagePortChannelImpl::ExtractMessagePortIDsWithoutQueueing,
           base::Passed(&channel_array)),
       base::Bind(&ServicePortProvider::PostMessageToBrowser, this, port_id,
-                 message));
+                 // We cast WebString to string16 before crossing threads.
+                 // for thread-safety.
+                 static_cast<base::string16>(message)));
 }
 
 void ServicePortProvider::closePort(blink::WebServicePortID port_id) {
   GetServicePortServicePtr()->ClosePort(port_id);
 }
 
 void ServicePortProvider::PostMessage(
     int32_t port_id,
     const mojo::String& message,
     mojo::Array<MojoTransferredMessagePortPtr> ports,
@@ skipping 36 matching lines @@
 
     // Setup channel for browser to post events back to this class.
     ServicePortServiceClientPtr client_ptr;
     binding_.Bind(GetProxy(&client_ptr));
     service_port_service_->SetClient(client_ptr.Pass());
   }
   return service_port_service_;
 }
 
 }  // namespace content