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

chrome/browser/search/search.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/search/search.h"
 
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/prefs/pref_service.h"
@@ skipping 387 matching lines @@
 
   FieldTrialFlags flags;
   return GetFieldTrialInfo(&flags) && GetBoolValueForFlagWithDefault(
       kEnableQueryExtractionFlagName, false, flags);
 #endif  // defined(OS_IOS) || defined(OS_ANDROID)
 }
 
 base::string16 ExtractSearchTermsFromURL(Profile* profile, const GURL& url) {
   if (url.is_valid() && url == GetSearchResultPrefetchBaseURL(profile)) {
     // InstantSearchPrerenderer has the search query for the Instant search base
     // 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);
   base::string16 search_terms;
   if (template_url)
     template_url->ExtractSearchTermsFromURL(url, &search_terms);
   return search_terms;
 }
 
 bool IsQueryExtractionAllowedForURL(Profile* profile, const GURL& url) {
@@ skipping 416 matching lines @@
 
 // Given a FieldTrialFlags object, returns the boolean value of the provided
 // flag.
 bool GetBoolValueForFlagWithDefault(const std::string& flag,
                                     bool default_value,
                                     const FieldTrialFlags& flags) {
   return !!GetUInt64ValueForFlagWithDefault(flag, default_value ? 1 : 0, flags);
 }
 
 }  // namespace chrome