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..0c1685324ca7288b3264fb69669bf4018f30df89 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) ||
+         IPC::ChannelMojo::ShouldBeUsed();
 }
 
 scoped_ptr<IPC::ChannelProxy> RenderProcessHostImpl::CreateChannelProxy(