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

ipc/mojo/ipc_channel_mojo.h

Index: ipc/mojo/ipc_channel_mojo.h
diff --git a/ipc/mojo/ipc_channel_mojo.h b/ipc/mojo/ipc_channel_mojo.h
index 696d744cd59a3c1cd41df38e98c68e588d1c5685..2fca377684f24dd83b11c8fecdc1ee661dfc185e 100644
--- a/ipc/mojo/ipc_channel_mojo.h
+++ b/ipc/mojo/ipc_channel_mojo.h
@@ -67,6 +67,9 @@ class IPC_MOJO_EXPORT ChannelMojo : public Channel,
     virtual void OnChannelCreated(base::WeakPtr<ChannelMojo> channel) = 0;
   };
 
+  // True if ChannelMojo should be used regardless of the flag.
+  static bool ShouldBeUsed();
+
   // Create ChannelMojo. A bootstrap channel is created as well.
   // |host| must not be null for server channels.
   static scoped_ptr<ChannelMojo> Create(Delegate* delegate,