Change a DCHECK to CHECK in chrome::ExtractSearchTermsFromURL().

chrome/browser/search/search.cc

Index: chrome/browser/search/search.cc
diff --git a/chrome/browser/search/search.cc b/chrome/browser/search/search.cc
index b1934df12235525a8029aa0c5ecee9999f95bb14..1c10dfa81b6f74321082fafb6422203168ccf0ce 100644
--- a/chrome/browser/search/search.cc
+++ b/chrome/browser/search/search.cc
@@ -408,8 +408,7 @@ base::string16 ExtractSearchTermsFromURL(Profile* profile, const GURL& url) {
     // page.

[Peter Kasting, 2014/05/01 20:21:02]

Nit: Add an explanation of when this can be NULL (e.g. "when testing", "if
window x has closed", etc. -- ideally not just "when function foo() returns
NULL").

     InstantSearchPrerenderer* prerenderer =
         InstantSearchPrerenderer::GetForProfile(profile);
-    DCHECK(prerenderer);
-    return prerenderer->get_last_query();
+    return prerenderer ? prerenderer->get_last_query() : base::string16();
   }
 
   TemplateURL* template_url = GetDefaultSearchProviderTemplateURL(profile);