Only log DICE disablement due to missing OAuth ID/secret once.

This reduces noise due to this warning, which can happen on the order
of 10 times at browser launch and more times thereafter.

Change-Id: Iecdb28d995eb5867a506f84112ef8fcf8794dbce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2160037Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#762047}

chrome/browser/signin/account_consistency_mode_manager.cc

@@ -197,8 +197,14 @@ AccountConsistencyModeManager::ComputeAccountConsistencyMethod(
   bool can_enable_dice_for_build = ignore_missing_oauth_client_for_testing_ ||
                                    google_apis::HasOAuthClientConfigured();
   if (!can_enable_dice_for_build) {
+    // Only log this once.
+    static bool logged_warning = []() {
       LOG(WARNING) << "Desktop Identity Consistency cannot be enabled as no "
                       "OAuth client ID and client secret have been configured.";
+      return true;
+    }();
+    ALLOW_UNUSED_LOCAL(logged_warning);
+
     return AccountConsistencyMethod::kDisabled;
   }