Change GetAccessToken APIs so that they don't pass const ref to blocks.

ios/public/provider/chrome/browser/signin/fake_chrome_identity_service.mm

Index: ios/public/provider/chrome/browser/signin/fake_chrome_identity_service.mm
diff --git a/ios/public/provider/chrome/browser/signin/fake_chrome_identity_service.mm b/ios/public/provider/chrome/browser/signin/fake_chrome_identity_service.mm
index 52d10a8a03fdfd914de06ec6ea1568f05ff37d67..6d7a522a734b77f065885097d9a393138133a0e0 100644
--- a/ios/public/provider/chrome/browser/signin/fake_chrome_identity_service.mm
+++ b/ios/public/provider/chrome/browser/signin/fake_chrome_identity_service.mm
@@ -23,7 +23,7 @@ void FakeGetAccessToken(ChromeIdentity*,
                         const std::string&,
                         const std::string&,
                         const std::set<std::string>&,
-                        const ios::AccessTokenCallback& callback) {
+                        ios::AccessTokenCallback callback) {
   base::mac::ScopedBlock<ios::AccessTokenCallback> safe_callback(
       [callback copy]);
 
@@ -215,7 +215,7 @@ void FakeChromeIdentityService::GetAccessToken(
     const std::string& client_id,
     const std::string& client_secret,
     const std::set<std::string>& scopes,
-    const ios::AccessTokenCallback& callback) {
+    ios::AccessTokenCallback callback) {
   FakeGetAccessToken(identity, client_id, client_secret, scopes, callback);
 }