Add extensions code to use common updater in components/update_client/

extensions/browser/extensions_browser_client.h

Index: extensions/browser/extensions_browser_client.h
diff --git a/extensions/browser/extensions_browser_client.h b/extensions/browser/extensions_browser_client.h
index 89763d9d7f48c15e5a0eb3e6d2e8cbe6449ced59..a5ddd8683fa0ad0d3f2dd1bc260899c40d0f60aa 100644
--- a/extensions/browser/extensions_browser_client.h
+++ b/extensions/browser/extensions_browser_client.h
@@ -8,6 +8,7 @@
 #include <string>
 #include <vector>
 
+#include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "extensions/browser/extension_event_histogram_value.h"
 #include "extensions/browser/extension_prefs_observer.h"
@@ -35,6 +36,10 @@ class URLRequest;
 class URLRequestJob;
 }
 
+namespace update_client {
+class UpdateClient;
+}
+
 namespace extensions {
 
 class ApiActivityMonitor;
@@ -236,6 +241,10 @@ class ExtensionsBrowserClient {
   virtual void AttachExtensionTaskManagerTag(content::WebContents* web_contents,
                                              ViewType view_type) {}
 
+  // Returns a new UpdateClient.
+  virtual scoped_refptr<update_client::UpdateClient> CreateUpdateClient(
+      content::BrowserContext* context);
+
   // Returns the single instance of |this|.
   static ExtensionsBrowserClient* Get();