Implemented 'Reset Search engines' feature.

chrome/browser/search_engines/template_url_service.h

Index: chrome/browser/search_engines/template_url_service.h
diff --git a/chrome/browser/search_engines/template_url_service.h b/chrome/browser/search_engines/template_url_service.h
index 2b8f5a249e4b2a21e896634bed9b491c52f5da89..60a372e7dbf475b70feb672c3c03b3e54b1c96b7 100644
--- a/chrome/browser/search_engines/template_url_service.h
+++ b/chrome/browser/search_engines/template_url_service.h
@@ -216,6 +216,13 @@ class TemplateURLService : public WebDataServiceConsumer,
   // NOTE: At least in unittest mode, this may return NULL.
   TemplateURL* GetDefaultSearchProvider();
 
+  // Clears user preferences describing the default search engine.
+  void ClearDefaultProviderFromPrefs();

[Peter Kasting, 2013/05/22 21:22:57]

If these two methods get called one after the other, why aren't they just one
method?

[vasilii, 2013/05/23 17:03:42]

Done.

+
+  // Clears non-extension URLs and reloads again prepopulated engines.
+  // Resets the default engine unless it's managed.

[Peter Kasting, 2013/05/22 21:22:57]

Nit: Grammar.  How about:

Resets the search providers to the prepopulated engines plus any
extension-supplied engines.  Also resets the default search engine unless it's
managed.

[vasilii, 2013/05/23 17:03:42]

Done.

+  bool ResetNonExtensionURLs();
+
   // Returns true if the default search is managed through group policy.
   bool is_default_search_managed() const { return is_default_search_managed_; }
 
@@ -582,6 +589,19 @@ class TemplateURLService : public WebDataServiceConsumer,
 
   void OnSyncedDefaultSearchProviderGUIDChanged();
 
+  // Adds |*template_urls| to |template_urls_| and sets up default search
+  // provider according to the internal logic.
+  // |template_urls| comes from database. The method takes ownership of
+  // |template_urls| and its elements.
+  // |default_search_provider| specifies URL inside |*template_urls|.

[Peter Kasting, 2013/05/22 21:22:57]

Nit: How about just:

Adds |template_urls| to |template_urls_| and sets up the default search
provider.  If |default_search_provider| is non-NULL, it must refer to one of the
|template_urls|, and will be used as the new default if there is no current
default.

[vasilii, 2013/05/23 17:03:42]

Done. Actually we set the default even if it's not NULL. But in both our
use-cases it's NULL.

+  void AddTemplateURLsAndSetupDefaultEngine(
+      TemplateURLVector* template_urls,
+      TemplateURL* default_search_provider);
+
+  // This sets the default search engine to FindNewDefaultSearchProvider(),
+  // if it's unmanaged and NULL.

[Peter Kasting, 2013/05/22 21:22:57]

Nit: How about:

If there is no current default search provider, sets the default to the result
of calling FindNewDefaultSearchProvider().

[vasilii, 2013/05/23 17:03:42]

Done.

+  void EnsureDefaultSearchProviderExists();
+
   content::NotificationRegistrar notification_registrar_;
   PrefChangeRegistrar pref_change_registrar_;