Add extension event histogram values for messaging, webRequest, and webview.

chrome/browser/extensions/api/messaging/message_service.h

Index: chrome/browser/extensions/api/messaging/message_service.h
diff --git a/chrome/browser/extensions/api/messaging/message_service.h b/chrome/browser/extensions/api/messaging/message_service.h
index e68b19ee3ab52349d5228afb224187e5bd9b40c1..9d209b2422b322ddd32371b3fe196d2c7f28b97e 100644
--- a/chrome/browser/extensions/api/messaging/message_service.h
+++ b/chrome/browser/extensions/api/messaging/message_service.h
@@ -186,8 +186,17 @@ class MessageService : public BrowserContextKeyedAPI,
   typedef std::map<int, PendingLazyBackgroundPageChannel>
       PendingLazyBackgroundPageChannelMap;
 
-  // Common among OpenChannel* variants.
-  void OpenChannelImpl(scoped_ptr<OpenChannelParams> params);
+  // Common implementation for opening a channel configured by |params|.
+  //
+  // |target_extension| will be non-null if |params->target_extension_id| is
+  // non-empty, that is, if the target is an extension, it must exist.
+  //
+  // |did_enqueue| will be true if the channel opening was delayed while
+  // waiting for an event page to start, false otherwise.
+  void OpenChannelImpl(content::BrowserContext* browser_context,
+                       scoped_ptr<OpenChannelParams> params,
+                       const Extension* target_extension,
+                       bool did_enqueue);
 
   void CloseChannelImpl(MessageChannelMap::iterator channel_iter,
                         int port_id,