Add WebContents source to methods in WebContentsDelegate

chrome/browser/prerender/prerender_manager.cc

Index: chrome/browser/prerender/prerender_manager.cc
diff --git a/chrome/browser/prerender/prerender_manager.cc b/chrome/browser/prerender/prerender_manager.cc
index 643e63bd0da9546bf1f99de262fd0f273c382fff..c7f84edd8f6ec580632dd9fccc1568982944d57a 100644
--- a/chrome/browser/prerender/prerender_manager.cc
+++ b/chrome/browser/prerender/prerender_manager.cc
@@ -191,9 +191,10 @@ class PrerenderManager::OnCloseWebContentsDeleter
     ScheduleWebContentsForDeletion(false);
   }
 
-  bool ShouldSuppressDialogs() override {
+  bool ShouldSuppressDialogs(WebContents* source) override {
     // Use this as a proxy for getting statistics on how often we fail to honor
     // the beforeunload event.
+    DCHECK_EQ(tab_, source);
     suppressed_dialog_ = true;
     return true;
   }