Introduce ChannelMojo

ipc/ipc_channel.h

Index: ipc/ipc_channel.h
diff --git a/ipc/ipc_channel.h b/ipc/ipc_channel.h
index bca3ea066c35f3477b37886fe16adf9e4ac5efbe..fbd4ae0aa0ac96d1b34e859a98cbf9dea576105b 100644
--- a/ipc/ipc_channel.h
+++ b/ipc/ipc_channel.h
@@ -170,6 +170,14 @@ class IPC_EXPORT Channel : public Sender {
   // listener.
   virtual base::ProcessId GetPeerPID() const = 0;
 
+  // Get its own process id. This value is told to the peer.

[Tom Sepez, 2014/08/07 18:36:22]

Can you elaborate on "this value is told to the peer."  Can an evil renderer lie
about this?  What happens then?

[Hajime Morrita, 2014/08/07 19:58:21]

Yes it can, as it can do that for current IPC implementation. (modulo secret
number check.) This just follows what existing IPC::Channel implementation does.
 
I don't know much about how the peer PID is used in the codebase.
One notable use it that this value is passed to
IPC::Listener::OnChannelConnected().

+  virtual base::ProcessId GetSelfPID() const = 0;
+
+  // Return connected ChannelHandle which the channel has owned.
+  // This method transfers the ownership to the caller
+  // so the channel isn't valid after the call.
+  virtual ChannelHandle TakePipeHandle() WARN_UNUSED_RESULT = 0;
+
   // Send a message over the Channel to the listener on the other end.
   //
   // |message| must be allocated using operator new.  This object will be