Implemented 'Reset Search engines' feature.

chrome/browser/search_engines/template_url_prepopulate_data.cc

Index: chrome/browser/search_engines/template_url_prepopulate_data.cc
diff --git a/chrome/browser/search_engines/template_url_prepopulate_data.cc b/chrome/browser/search_engines/template_url_prepopulate_data.cc
index 235f621966a62123151a531121ec714b2b6dfccf..efbb266f60d75054491325c8be38a0273f8bed8f 100644
--- a/chrome/browser/search_engines/template_url_prepopulate_data.cc
+++ b/chrome/browser/search_engines/template_url_prepopulate_data.cc
@@ -1197,6 +1197,16 @@ void GetPrepopulatedTemplateFromPrefs(Profile* profile,
   }
 }
 
+void ClearPrepopulatedEnginesInPrefs(Profile* profile) {
+  if (!profile)
+    return;
+
+  PrefService* prefs = profile->GetPrefs();
+  DCHECK(prefs);
+  prefs->ClearPref(prefs::kSearchProviderOverrides);
+  prefs->ClearPref(prefs::kSearchProviderOverridesVersion);

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

These prefs are supposed to only be set by tests and by the master prefs.  Are
you sure clearing them is correct?  You may want to ping joaodasilva about the
master prefs side of this.

[Joao da Silva, 2013/05/23 08:54:10]

As Peter mentioned, these prefs can only come from the master_preferences. The
master_preferences are sort-of a template of the user Preferences file, that is
imported only once during the first run. It is used by administrators to
preconfigure settings, including the list of search providers.

So these prefs should *not* be cleared when the user cleans up his profile. IMO
the right thing to do is to clean up the search providers database, and then
populate it again as if the profile is new; that should import the
"search_provider_overrides" again, if they exist in that Profile's preferences;
otherwise it should import the default initial providers.

Peter, does this make sense to you too? :-)

[Joao da Silva, 2013/05/23 09:12:51]

I wasn't looking at this from the malware prevention POV. After discussing with
Dominic I now think it's fine to clean it up.

Whatever is imported from master_preferences can easily be modified by the user,
so there is no strong enforcement of those settings like we do for policies. And
malware can modify the master_preferences file just as easily as the
preferences; so I'm fine with cleaning this up.

On the enterprise side, we may come to deprecate master_preferences if they
become an attack vector. We can add a few new policies to do the same that the
master_prefs are usually used for.

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

The purpose of this feature is to recover Chrome after some malware's spoiled
user settings. Therefore we definitely want to reset them for current profile.

+}
+
 // The caller owns the returned TemplateURL.
 TemplateURL* MakePrepopulatedTemplateURLFromPrepopulateEngine(
     Profile* profile,