app_shell: Add ShellContentRendererClient

extensions/common/extensions_client.cc

Index: extensions/common/extensions_client.cc
diff --git a/extensions/common/extensions_client.cc b/extensions/common/extensions_client.cc
index ccca164a5ff5e1f3f77b21ff77ebf00589dbe2eb..89795b86e45cb0df34392340de375773dad8cad0 100644
--- a/extensions/common/extensions_client.cc
+++ b/extensions/common/extensions_client.cc
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "base/basictypes.h"
+#include "base/logging.h"
 #include "extensions/common/extensions_client.h"
 
 namespace extensions {
@@ -14,6 +15,7 @@ ExtensionsClient* g_client = NULL;
 }  // namespace
 
 ExtensionsClient* ExtensionsClient::Get() {
+  DCHECK(g_client);
   return g_client;
 }