Rename notification_id() to disambiguate its meaning

chrome/browser/notifications/notification.h

Index: chrome/browser/notifications/notification.h
diff --git a/chrome/browser/notifications/notification.h b/chrome/browser/notifications/notification.h
index 18997a697cc1cdfd9a0fd1b0bedb46e28b795241..d2a9d4aef8e87316a2a2fc024375e650899c5864 100644
--- a/chrome/browser/notifications/notification.h
+++ b/chrome/browser/notifications/notification.h
@@ -82,7 +82,8 @@ class Notification : public message_center::Notification {
   // A url for the image to be shown (optional).
   const GURL& image_url() const { return image_url_; }
 
-  std::string notification_id() const { return delegate()->id(); }
+  // Id of the delegate embedded inside this instance.
+  std::string delegate_id() const { return delegate()->id(); }
   int process_id() const { return delegate()->process_id(); }
 
   content::WebContents* GetWebContents() const {