ipc_channel: warn if someone forgets to check the result of Connect()

I found a test that was doing this.

Review URL: http://codereview.chromium.org/3759004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@63083 0039d316-1c4b-4281-b951-d872f2087c98

diff --git a/ipc/ipc_channel.h b/ipc/ipc_channel.h
index dc5031e1..65ed9f0 100644
--- a/ipc/ipc_channel.h
+++ b/ipc/ipc_channel.h

@@ -6,6 +6,7 @@
 #define IPC_IPC_CHANNEL_H_
 #pragma once
 
+#include "base/compiler_specific.h"
 #include "ipc/ipc_message.h"
 
 namespace IPC {
@@ -68,7 +69,7 @@
   // connect to a pre-existing pipe.  Note, calling Connect()
   // will not block the calling thread and may complete
   // asynchronously.
-  bool Connect();
+  bool Connect() WARN_UNUSED_RESULT;
 
   // Close this Channel explicitly.  May be called multiple times.
   void Close();