Add a URL param to indicate group selection in Instant field trial.

chrome/browser/search_engines/search_provider_install_data.cc

Index: chrome/browser/search_engines/search_provider_install_data.cc
diff --git a/chrome/browser/search_engines/search_provider_install_data.cc b/chrome/browser/search_engines/search_provider_install_data.cc
index 4f9994ecd1ed71dc63e60ff29a7d7e21ef2ae542..92b18e0425a19a7d574aa6dd6b402e380508628f 100644
--- a/chrome/browser/search_engines/search_provider_install_data.cc
+++ b/chrome/browser/search_engines/search_provider_install_data.cc
@@ -154,6 +154,7 @@ static bool IsSameOrigin(const GURL& requested_origin,
   DCHECK(requested_origin == requested_origin.GetOrigin());
   return template_url && requested_origin ==
       TemplateURLService::GenerateSearchURLUsingTermsData(
+          NULL,
           template_url,
           search_terms_data).GetOrigin();
 }
@@ -277,7 +278,7 @@ void SearchProviderInstallData::SetDefault(const TemplateURL* template_url) {
 
   IOThreadSearchTermsData search_terms_data(google_base_url_);
   const GURL url(TemplateURLService::GenerateSearchURLUsingTermsData(
-      template_url, search_terms_data));
+      NULL, template_url, search_terms_data));
   if (!url.is_valid() || !url.has_host()) {
     default_search_origin_.clear();
     return;