sync: Per-type update application

sync/sessions/sync_session_context.h

Index: sync/sessions/sync_session_context.h
diff --git a/sync/sessions/sync_session_context.h b/sync/sessions/sync_session_context.h
index d195943686e9068339ce4cecb512fcd157e890d6..5995ab151dbcbba209872310ce532fcfa3030da7 100644
--- a/sync/sessions/sync_session_context.h
+++ b/sync/sessions/sync_session_context.h
@@ -3,15 +3,12 @@
 // found in the LICENSE file.
 
 // SyncSessionContext encapsulates the contextual information and engine
-// components specific to a SyncSession. A context is accessible via
-// a SyncSession so that session SyncerCommands and parts of the engine have
-// a convenient way to access other parts. In this way it can be thought of as
-// the surrounding environment for the SyncSession. The components of this
-// environment are either valid or not valid for the entire context lifetime,
-// or they are valid for explicitly scoped periods of time by using Scoped
-// installation utilities found below. This means that the context assumes no
-// ownership whatsoever of any object that was not created by the context
-// itself.
+// components specific to a SyncSession.  Unlike the SyncSession, the context
+// can be reused across several sync cycles.
+//
+// The context does not take ownership of its pointer members.  It's up to
+// the surrounding classes to ensure those members remain valid while the
+// context is in use.
 //
 // It can only be used from the SyncerThread.
 
@@ -70,8 +67,8 @@ class SYNC_EXPORT_PRIVATE SyncSessionContext {
     return directory_;
   }
 
-  const ModelSafeRoutingInfo& routing_info() const {
-    return routing_info_;
+  ModelTypeSet enabled_types() const {
+    return enabled_types_;
   }
 
   void set_routing_info(const ModelSafeRoutingInfo& routing_info);
@@ -84,10 +81,6 @@ class SYNC_EXPORT_PRIVATE SyncSessionContext {
     return &commit_contributor_map_;
   }
 
-  const std::vector<scoped_refptr<ModelSafeWorker> >& workers() const {
-    return workers_;
-  }
-
   ExtensionsActivity* extensions_activity() {
     return extensions_activity_.get();
   }
@@ -159,9 +152,9 @@ class SYNC_EXPORT_PRIVATE SyncSessionContext {
   ServerConnectionManager* const connection_manager_;
   syncable::Directory* const directory_;
 
-  // A cached copy of SyncBackendRegistrar's routing info.
-  // Must be updated manually when SBR's state is modified.
-  ModelSafeRoutingInfo routing_info_;
+  // The set of enabled types.  Derrived from the routing info set with
+  // set_routing_info().
+  ModelTypeSet enabled_types_;
 
   // A map of 'update handlers', one for each enabled type.
   // This must be kept in sync with the routing info.  Our temporary solution to
@@ -180,7 +173,7 @@ class SYNC_EXPORT_PRIVATE SyncSessionContext {
   STLValueDeleter<CommitContributorMap> commit_contributor_deleter_;
 
   // The set of ModelSafeWorkers.  Used to execute tasks of various threads.
-  std::vector<scoped_refptr<ModelSafeWorker> > workers_;
+  std::map<ModelSafeGroup, scoped_refptr<ModelSafeWorker> > workers_;
 
   // We use this to stuff extensions activity into CommitMessages so the server
   // can correlate commit traffic with extension-related bookmark mutations.