Mojo: Add the ability to hook up a channel to the embedder API.

mojo/public/system/core_private.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/public/system/core_private.h"
 
 #include <assert.h>
 #include <stddef.h>
 
 static mojo::Core* g_core = NULL;
@@ skipping 110 matching lines @@
   return g_core->EndReadData(data_pipe_consumer_handle, num_elements_read);
 }
 
 }  // extern "C"
 
 namespace mojo {
 
 Core::~Core() {
 }
 
+// static
 void Core::Init(Core* core) {
   assert(!g_core);
   g_core = core;
 }
 
+// static
+Core* Core::Get() {
+  return g_core;
+}
+
+// static
+void Core::Reset() {
+  g_core = NULL;
+}
+
 }  // namespace mojo