[Sync::USS] Simplify ClientTagBasedModelTypeProcessor::ReportError()

This CL doesn't introduce any behavioral change. It's a pure
refactoring CL that simplifies the code in ReportError().

Change-Id: I24295b8266d013e639e5a0dd5f5b23a475a5b27d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1588566
Commit-Queue: Mohamed Amir Yosef <mamir@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Auto-Submit: Mohamed Amir Yosef <mamir@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660351}

components/sync/model_impl/client_tag_based_model_type_processor.cc

@@ -293,8 +293,9 @@ void ClientTagBasedModelTypeProcessor::ReportError(const ModelError& error) {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 
   // Ignore all errors after the first.
-  if (model_error_)
+  if (model_error_) {
     return;
+  }
 
   model_error_ = error;
 
@@ -307,14 +308,14 @@ void ClientTagBasedModelTypeProcessor::ReportError(const ModelError& error) {
     DisconnectSync();
   }
 
-  if (start_callback_) {
-    // Tell sync about the error instead of connecting.
-    ConnectIfReady();
-  } else if (activation_request_.error_handler) {
-    // Connecting was already initiated; just tell sync about the error instead
-    // of going through ConnectIfReady().
+  // Shouldn't connect anymore.
+  start_callback_.Reset();
+  if (activation_request_.error_handler) {
+    // Tell sync about the error.
     activation_request_.error_handler.Run(error);
   }
+  // If the error handler isn't ready yet, we defer reporting the error until it
+  // becomes available which happens in ConnectIfReady() upon OnSyncStarting().
 }
 
 base::Optional<ModelError> ClientTagBasedModelTypeProcessor::GetError() const {