Fall back to local page if online NTP fails to load.

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 142 matching lines @@
 bool IsInstantURL(const GURL& url, Profile* profile) {
   TemplateURL* template_url = GetDefaultSearchProviderTemplateURL(profile);
   if (!template_url)
     return false;
 
   const TemplateURLRef& instant_url_ref = template_url->instant_url_ref();
   const bool extended_api_enabled = IsInstantExtendedAPIEnabled();
   GURL effective_url = url;
 
   if (IsCommandLineInstantURL(url))
-    effective_url = CoerceCommandLineURLToTemplateURL(url, instant_url_ref,
-                                                      kDisableStartMargin);
+    return true;

[samarth, 2013/04/30 17:10:33]

I assume this was for debugging. (Shouldn't be necessary btw. Just
--instant-url='http://does/not/exist/?espv=2' should work.)

[David Black, 2013/04/30 23:09:08]

No, this is necessary, as that URL otherwise doesn't work. 
CoerceCommandLineURLToTemplateURL doesn't change the path, and below we check
MatchesOriginAndPath vs the built-in template URL.  So, if it's not a /search or
/webhp page then no go.  It took me a while to debug why on earth using
--instant-url="https://www.google.com/notarealpah?espv=2" was generating a bunch
of really mysterious behavior.

[samarth, 2013/05/01 06:26:47]

In that case, you should change Coerce... to also change the path.  I think you
still want search term extraction, etc. to still work even if you're using a
custom path.

[David Black, 2013/05/02 00:49:45]

Search term extraction still does work.  It's only here in this function where
we coerce a URL and then verify its path matches the vanilla template URL.  It
seems quite clear to me that a function called IsInstantURL should always simply
return true if IsCommandLineInstantURL returns true - having any coercing going
on at all in this function makes no sense to me.

 
   if (!effective_url.is_valid())
     return false;
 
   if (extended_api_enabled && !effective_url.SchemeIsSecure())
     return false;
 
   if (extended_api_enabled &&
       !template_url->HasSearchTermsReplacementKey(effective_url))
     return false;
@@ skipping 425 matching lines @@
 
   GURL instant_url = TemplateURLRefToGURL(template_url->instant_url_ref(),
                                           kDisableStartMargin);
   // Extended mode instant requires a search terms replacement key.
   return instant_url.is_valid() &&
          (!IsInstantExtendedAPIEnabled() ||
           template_url->HasSearchTermsReplacementKey(instant_url));
 }
 
 }  // namespace chrome