[Sync] SyncEngine refactor part 1: interfaces.

components/sync/engine/sync_engine_host.h

Index: components/sync/engine/sync_engine_host.h
diff --git a/components/sync/driver/sync_frontend.h b/components/sync/engine/sync_engine_host.h
similarity index 88%
rename from components/sync/driver/sync_frontend.h
rename to components/sync/engine/sync_engine_host.h
index c68b96a8801b606e9a8289bec10c9a2cc34fdfe4..408fbbc99551fbe04fa03e61defad5f45c6c15e8 100644
--- a/components/sync/driver/sync_frontend.h
+++ b/components/sync/engine/sync_engine_host.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef COMPONENTS_SYNC_DRIVER_SYNC_FRONTEND_H_
-#define COMPONENTS_SYNC_DRIVER_SYNC_FRONTEND_H_
+#ifndef COMPONENTS_SYNC_ENGINE_SYNC_ENGINE_HOST_H_
+#define COMPONENTS_SYNC_ENGINE_SYNC_ENGINE_HOST_H_
 
 #include <string>
 
@@ -26,15 +26,15 @@ struct CommitCounters;
 struct StatusCounters;
 struct UpdateCounters;
 
-// SyncFrontend is the interface used by SyncBackendHost to communicate with
-// the entity that created it and, presumably, is interested in sync-related
-// activity.
-// NOTE: All methods will be invoked by a SyncBackendHost on the same thread
-// used to create that SyncBackendHost.
-class SyncFrontend {
+// SyncEngineHost is the interface used by SyncEngine to communicate with the
+// entity

[skym, 2016/12/02 20:54:55]

Line breaks here should get cleaned up.

[maxbogue, 2016/12/02 23:59:28]

Done.

+// that created it and, presumably, is interested in sync-related activity.
+// NOTE: All methods will be invoked by a SyncEngine on the same thread used to

[skym, 2016/12/02 20:54:55]

I worry that this comment is pretty confusing if you don't already know what's
going on.

The way I see it, SyncEngineHost is essentially the list of the things that the
engine should notify the driver component of when they occur. It is the engine's
responsibility to make sure these get called at the appropriate times.

[maxbogue, 2016/12/02 23:59:28]

Changed it, PTAL.

+// create that SyncEngine.
+class SyncEngineHost {
  public:
-  SyncFrontend();
-  virtual ~SyncFrontend();
+  SyncEngineHost();
+  virtual ~SyncEngineHost();
 
   // The backend has completed initialization and it is now ready to
   // accept and process changes.  If success is false, initialization
@@ -54,7 +54,7 @@ class SyncFrontend {
 
   // Informs the frontned of some network event.  These notifications are

[skym, 2016/12/02 20:54:55]

This misspelling evaded you!

[maxbogue, 2016/12/02 23:59:28]

I'm personally offended by its audacity.

   // disabled by default and must be enabled through an explicit request to the
-  // SyncBackendHost.
+  // SyncEngine.
   //
   // It's disabld by default to avoid copying data across threads when no one
   // is listening for it.
@@ -91,7 +91,7 @@ class SyncFrontend {
   // called when the first sensitive data type is setup by the user and anytime
   // the passphrase is changed by another synced client. |reason| denotes why
   // the passphrase was required. |pending_keys| is a copy of the
-  // cryptographer's pending keys to be passed on to the frontend in order to
+  // cryptographer's pending keys to be passed on to the host in order to
   // be cached.
   virtual void OnPassphraseRequired(
       PassphraseRequiredReason reason,
@@ -124,7 +124,7 @@ class SyncFrontend {
   // Called to perform migration of |types|.
   virtual void OnMigrationNeededForTypes(ModelTypeSet types) = 0;
 
-  // Inform the Frontend that new datatypes are available for registration.
+  // Inform the host that new datatypes are available for registration.

[skym, 2016/12/02 20:54:55]

I like the 'Called when...' phrasing more than this.

[maxbogue, 2016/12/02 23:59:28]

Done.

   virtual void OnExperimentsChanged(const Experiments& experiments) = 0;
 
   // Called when the sync cycle returns there is an user actionable error.
@@ -141,4 +141,4 @@ class SyncFrontend {
 
 }  // namespace syncer
 
-#endif  // COMPONENTS_SYNC_DRIVER_SYNC_FRONTEND_H_
+#endif  // COMPONENTS_SYNC_ENGINE_SYNC_ENGINE_HOST_H_