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

mojo/public/system/core_private.cc

Index: mojo/public/system/core_private.cc
diff --git a/mojo/public/system/core_private.cc b/mojo/public/system/core_private.cc
index 3b657ee0e99c82d0e8f83e00837ffb12236e59e9..f0bc3f156bee96d9d967ae6eaa3d7ebff28da8ea 100644
--- a/mojo/public/system/core_private.cc
+++ b/mojo/public/system/core_private.cc
@@ -128,9 +128,20 @@ 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