Cleanup: Do not pass a non-const ref in RequestDesktopNotificationPermission.

chrome/browser/chrome_content_browser_client.cc

Index: chrome/browser/chrome_content_browser_client.cc
diff --git a/chrome/browser/chrome_content_browser_client.cc b/chrome/browser/chrome_content_browser_client.cc
index 10c86804ebb0a9b82d170523f813663b1c6a7c08..9758cdda9f9433caacd54a66fa8ed4659d7f468b 100644
--- a/chrome/browser/chrome_content_browser_client.cc
+++ b/chrome/browser/chrome_content_browser_client.cc
@@ -2029,7 +2029,7 @@ content::MediaObserver* ChromeContentBrowserClient::GetMediaObserver() {
 void ChromeContentBrowserClient::RequestDesktopNotificationPermission(
     const GURL& source_origin,
     content::RenderFrameHost* render_frame_host,
-    base::Closure& callback) {
+    const base::Closure& callback) {
 #if defined(ENABLE_NOTIFICATIONS)
   // Skip showing the infobar if the request comes from an extension, and that
   // extension has the 'notify' permission. (If the extension does not have the