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

content/browser/renderer_host/render_process_host_impl.cc

Index: content/browser/renderer_host/render_process_host_impl.cc
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index ba098ddaae84ad25569730acae126a2ea6920a57..70936a95d44f0833efc0c3aaf110cffedaf08334 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -648,7 +648,8 @@ bool RenderProcessHostImpl::Init() {
 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(