Fix DCHECK in GetExperimentalAuthenticationKey with local sync enabled

- Return nullptr key when local sync is enabled and avoid DCHECK

Bug: 1023827
Change-Id: I73fac96233ff0b17611b8d0ffb150d9977417d50
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1911218
Commit-Queue: Alex Chau <alexchau@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714630}

chrome/browser/sync/test/integration/local_sync_test.cc

@@ -19,6 +19,7 @@
 #include "components/browser_sync/browser_sync_switches.h"
 #include "components/sync/driver/profile_sync_service.h"
 #include "components/sync/driver/sync_driver_switches.h"
+#include "crypto/ec_private_key.h"
 
 namespace {
 
@@ -75,6 +76,7 @@ IN_PROC_BROWSER_TEST_F(LocalSyncTest, ShouldStart) {
   ASSERT_TRUE(SyncTransportActiveChecker(service).Wait());
 
   EXPECT_TRUE(service->IsLocalSyncEnabled());
+  EXPECT_FALSE(service->GetExperimentalAuthenticationKey());
 
   // Verify certain features are disabled.
   EXPECT_FALSE(send_tab_to_self::IsUserSyncTypeActive(browser()->profile()));

components/sync/driver/profile_sync_service.cc

@@ -1954,7 +1954,8 @@ std::string ProfileSyncService::GetExperimentalAuthenticationSecret() const {
   // when usually all except keystore keys are guaranteed to be available.
   // Keystore keys are usually available initially too, but in rare cases they
   // should arrive in later sync cycles.
-  if (last_keystore_key_.empty()) {
+  // GAIA ID is not available with local sync enabled.
+  if (last_keystore_key_.empty() || IsLocalSyncEnabled()) {
     return std::string();
   }
 

components/sync/driver/profile_sync_service_unittest.cc

@@ -1503,5 +1503,15 @@ TEST_F(ProfileSyncServiceTest, GetExperimentalAuthenticationKey) {
   EXPECT_EQ(kExpectedPrivateKeyInfo, actual_private_key);
 }
 
+TEST_F(ProfileSyncServiceTest, GetExperimentalAuthenticationKeyLocalSync) {
+  CreateServiceWithLocalSyncBackend();
+  InitializeForNthSync();
+  EXPECT_EQ(SyncService::TransportState::ACTIVE,
+            service()->GetTransportState());
+
+  EXPECT_TRUE(service()->GetExperimentalAuthenticationSecretForTest().empty());
+  EXPECT_FALSE(service()->GetExperimentalAuthenticationKey());
+}
+
 }  // namespace
 }  // namespace syncer