[Sync] Clean up SMTP startup flow.

components/sync/model_impl/shared_model_type_processor.h

Index: components/sync/model_impl/shared_model_type_processor.h
diff --git a/components/sync/model_impl/shared_model_type_processor.h b/components/sync/model_impl/shared_model_type_processor.h
index b0e7de776b37aed8af3892c8c7b9e8e6e27d57c1..68c8bcd80bb5b054dbb87d0fa3c222e6700312da 100644
--- a/components/sync/model_impl/shared_model_type_processor.h
+++ b/components/sync/model_impl/shared_model_type_processor.h
@@ -27,6 +27,7 @@
 #include "components/sync/protocol/sync.pb.h"
 
 namespace syncer {
+
 class CommitQueue;
 class ProcessorEntityTracker;
 
@@ -73,13 +74,8 @@ class SharedModelTypeProcessor : public ModelTypeProcessor,
   friend class ModelTypeDebugInfo;
   friend class SharedModelTypeProcessorTest;
 
-  using EntityMap =
-      std::map<std::string, std::unique_ptr<ProcessorEntityTracker>>;
-  using UpdateMap = std::map<std::string, std::unique_ptr<UpdateResponseData>>;
-
-  // Whether the preconditions to connect are met. Note: returns true if we have
-  // already connected.
-  bool ConnectPreconditionsMet() const;
+  // Returns true if the model is ready or encountered an error.
+  bool IsModelReadyOrError() const;
 
   // If preconditions are met, inform sync that we are ready to connect.
   void ConnectIfReady();
@@ -146,15 +142,16 @@ class SharedModelTypeProcessor : public ModelTypeProcessor,
   // Stores the start callback in between OnSyncStarting() and ReadyToConnect().
   StartCallback start_callback_;
 
-  // A cache for any error that may occur during startup and should be passed
-  // into the |start_callback_|.
-  base::Optional<ModelError> start_error_;
+  // The first model error that occurred, if any. Stored to track model state
+  // and so it can be passed to sync if it happened prior to sync being ready.
+  base::Optional<ModelError> model_error_;
 
-  // Indicates whether the metadata has finished loading.
-  bool is_metadata_loaded_ = false;
+  // Whether we're waiting for the model to provide metadata.
+  bool waiting_for_metadata_ = true;
 
-  // Indicates whether data for any initial pending commits has been loaded.
-  bool is_initial_pending_data_loaded_ = false;
+  // Whether we're waiting for the model to provide initial commit data. Starts
+  // as false but will be set to true if we detect it's necessary to load data.
+  bool waiting_for_pending_data_ = false;
 
   // Reference to the CommitQueue.
   //
@@ -166,7 +163,7 @@ class SharedModelTypeProcessor : public ModelTypeProcessor,
   // A map of client tag hash to sync entities known to this processor. This
   // should contain entries and metadata for most everything, although the
   // entities may not always contain model type data/specifics.
-  EntityMap entities_;
+  std::map<std::string, std::unique_ptr<ProcessorEntityTracker>> entities_;
 
   // The bridge wants to communicate entirely via storage keys that is free to
   // define and can understand more easily. All of the sync machinery wants to