Enable "Let me choose what to sync" checkbox in gaia sign in page.

chrome/browser/ui/webui/sync_promo/sync_promo_ui.cc

Index: chrome/browser/ui/webui/sync_promo/sync_promo_ui.cc
diff --git a/chrome/browser/ui/webui/sync_promo/sync_promo_ui.cc b/chrome/browser/ui/webui/sync_promo/sync_promo_ui.cc
index d1029fa870ba0eb7ef36e18d94473f9b6fbfdf85..d5acc7a55e7bc8dd29ece74f9ed07e80187345d6 100644
--- a/chrome/browser/ui/webui/sync_promo/sync_promo_ui.cc
+++ b/chrome/browser/ui/webui/sync_promo/sync_promo_ui.cc
@@ -50,9 +50,9 @@ const char kSyncPromoQueryKeyContinue[] = "continue";
 const char kSyncPromoQueryKeyNextPage[] = "next_page";
 const char kSyncPromoQueryKeySource[] = "source";
 
-// TODO(rogerta): It would be better to use about:blank, but until that is
-// supported by Gaia this blank continue URL will be used.
-const char kContinueUrl[] = "http://www.google.com/gen_204";
+// Gaia cannot support about:blank as a continue URL, so using a hosted blank
+// page instead.
+const char kContinueUrl[] = "http://www.google.com/chrome/blank.html";
 
 // The maximum number of times we want to show the sync promo at startup.
 const int kSyncPromoShowAtStartupMaximum = 10;
@@ -240,7 +240,7 @@ GURL SyncPromoUI::GetSyncPromoURL(const GURL& next_page,
     // which of the chrome sign in access points was used to sign the userr in.
     // See OneClickSigninHelper for details.
     url_string = GaiaUrls::GetInstance()->service_login_url();
-    url_string.append("?service=chromiumsync");
+    url_string.append("?service=chromiumsync&sarp=1&rm=hide&fpc=1");
 
     std::string continue_url = base::StringPrintf("%s?%s=%d",
         kContinueUrl, kSyncPromoQueryKeySource, static_cast<int>(source));
@@ -268,9 +268,10 @@ GURL SyncPromoUI::GetSyncPromoURL(const GURL& next_page,
 
 // static
 GURL SyncPromoUI::GetNextPageURLForSyncPromoURL(const GURL& url) {
+  const char* key_name = UseWebBasedSigninFlow() ? kSyncPromoQueryKeyContinue :
+      kSyncPromoQueryKeyNextPage;
   std::string value;
-  if (chrome_common_net::GetValueForKeyInQuery(
-          url, kSyncPromoQueryKeyNextPage, &value)) {
+  if (chrome_common_net::GetValueForKeyInQuery(url, key_name, &value)) {
     return GURL(value);
   }
   return GURL();