Improve FakeSigninManager::DoSignout() - Check IsAuthenticated

This brings the fake a little closer to real SigninManager. The added
behavior is critical to *upcoming tests for the IdentityMager
ClearPrimaryAccount() (aka signout) API.

*https://chromium-review.googlesource.com/c/chromium/src/+/1154985

Bug: 806781
Change-Id: I4d533e67223dfe4bce6ca26eee7aea6f7cc075fd
Reviewed-on: https://chromium-review.googlesource.com/1160495Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Chrome Cunningham (In Paris) <chcunningham@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580500}

components/signin/core/browser/fake_signin_manager.cc

@@ -89,6 +89,22 @@ void FakeSigninManager::DoSignOut(
     signin_metrics::ProfileSignout signout_source_metric,
     signin_metrics::SignoutDelete signout_delete_metric,
     RemoveAccountsOption remove_option) {
+  if (!IsAuthenticated()) {
+    if (AuthInProgress()) {
+      // If the user is in the process of signing in, then treat a call to
+      // SignOut as a cancellation request.
+      GoogleServiceAuthError error(GoogleServiceAuthError::REQUEST_CANCELED);
+      HandleAuthError(error);
+    } else {
+      // Clean up our transient data and exit if we aren't signed in.
+      // This avoids a perf regression from clearing out the TokenDB if
+      // SignOut() is invoked on startup to clean up any incomplete previous
+      // signin attempts.
+      ClearTransientSigninData();
+    }
+    return;
+  }
+
   if (IsSignoutProhibited())
     return;
   set_auth_in_progress(std::string());