arc: Prepare ArcAuthEndpoint flag for finch experiment.

chrome/browser/chromeos/arc/arc_auth_code_fetcher.cc

Index: chrome/browser/chromeos/arc/arc_auth_code_fetcher.cc
diff --git a/chrome/browser/chromeos/arc/arc_auth_code_fetcher.cc b/chrome/browser/chromeos/arc/arc_auth_code_fetcher.cc
index 2ab0774eb64249fbbff2465a10a15646eadcb63e..24b58c91b55822e5fa292f1a972c1f988f0d0fd7 100644
--- a/chrome/browser/chromeos/arc/arc_auth_code_fetcher.cc
+++ b/chrome/browser/chromeos/arc/arc_auth_code_fetcher.cc
@@ -38,19 +38,19 @@ constexpr char kLoginScopedToken[] = "login_scoped_token";
 constexpr char kGetAuthCodeHeaders[] =
     "Content-Type: application/json; charset=utf-8";
 constexpr char kContentTypeJSON[] = "application/json";
+constexpr char kEndPoint[] =
+    "https://www.googleapis.com/oauth2/v4/ExchangeToken";
 
 }  // namespace
 
 ArcAuthCodeFetcher::ArcAuthCodeFetcher(
     ArcAuthCodeFetcherDelegate* delegate,
     net::URLRequestContextGetter* request_context_getter,
-    Profile* profile,
-    const std::string& auth_endpoint)
+    Profile* profile)
     : OAuth2TokenService::Consumer(kConsumerName),
       delegate_(delegate),
       request_context_getter_(request_context_getter),
-      profile_(profile),
-      auth_endpoint_(auth_endpoint) {
+      profile_(profile) {
   // Get token service and account ID to fetch auth tokens.
   ProfileOAuth2TokenService* const token_service =
       ProfileOAuth2TokenServiceFactory::GetForProfile(profile_);
@@ -86,9 +86,8 @@ void ArcAuthCodeFetcher::OnGetTokenSuccess(
   std::string request_string;
   base::JSONWriter::Write(request_data, &request_string);
 
-  DCHECK(!auth_endpoint_.empty());
-  auth_code_fetcher_ = net::URLFetcher::Create(0, GURL(auth_endpoint_),
-                                               net::URLFetcher::POST, this);
+  auth_code_fetcher_ =
+      net::URLFetcher::Create(0, GURL(kEndPoint), net::URLFetcher::POST, this);
   auth_code_fetcher_->SetRequestContext(request_context_getter_);
   auth_code_fetcher_->SetUploadData(kContentTypeJSON, request_string);
   auth_code_fetcher_->SetLoadFlags(net::LOAD_DISABLE_CACHE |