ChannelMojo: Add ChannelMojo::CanBeUsed() to enable it incrementally

content/browser/renderer_host/render_process_host_impl.cc

 // Copyright (c) 2012 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.
 
 // Represents the browser side of the browser <--> renderer communication
 // channel. There will be one RenderProcessHost per renderer process.
 
 #include "content/browser/renderer_host/render_process_host_impl.h"
 
 #include <algorithm>
@@ skipping 630 matching lines @@
   power_monitor_broadcaster_.Init();
 
   is_initialized_ = true;
   init_time_ = base::TimeTicks::Now();
   return true;
 }
 
 bool RenderProcessHostImpl::ShouldUseMojoChannel() const {
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
-  return command_line.HasSwitch(switches::kEnableRendererMojoChannel);
+  return command_line.HasSwitch(switches::kEnableRendererMojoChannel) ||

[viettrungluu, 2014/10/20 21:50:11]

Should this be "&&" instead of "||"?

My interpretation of the flag would be to "enable if possible" (which means
"&&").

Otherwise, this is more of a "force enable" flag ("enable even if it's not
entirely supported").

Another possibility would be to replace it with kDisableRendererMojoChannel, and
do |ChannelMojoHost::CanBeUsed() &&
!command_line.HasSwitch(switches::kDisableRendererMojoChannel)|.

[Hajime Morrita, 2014/10/20 23:06:50]

My intention here is that let people try this flag locally + turn
the feature on some platform. So I want to force it. 
Renamed ShouldBeUsed().

+         ChannelMojoHost::CanBeUsed();
 }
 
 scoped_ptr<IPC::ChannelProxy> RenderProcessHostImpl::CreateChannelProxy(
     const std::string& channel_id) {
   scoped_refptr<base::SingleThreadTaskRunner> runner =
       BrowserThread::GetMessageLoopProxyForThread(BrowserThread::IO);
   if (ShouldUseMojoChannel()) {
     VLOG(1) << "Mojo Channel is enabled on host";
     if (!channel_mojo_host_) {
       channel_mojo_host_.reset(new IPC::ChannelMojoHost(
@@ skipping 1568 matching lines @@
 
 void RenderProcessHostImpl::DecrementWorkerRefCount() {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   DCHECK_GT(worker_ref_count_, 0);
   --worker_ref_count_;
   if (worker_ref_count_ == 0)
     Cleanup();
 }
 
 }  // namespace content