[Sync] Refactored ProfileSyncService and remove its backend() function

chrome/browser/sync/glue/sync_backend_host.h

Index: chrome/browser/sync/glue/sync_backend_host.h
diff --git a/chrome/browser/sync/glue/sync_backend_host.h b/chrome/browser/sync/glue/sync_backend_host.h
index 964f7a5d06e03a8c72512c9ae31186bf28340644..9cf0c5624d59b1f89a0bbc03de66e2db2b7b6b32 100644
--- a/chrome/browser/sync/glue/sync_backend_host.h
+++ b/chrome/browser/sync/glue/sync_backend_host.h
@@ -107,7 +107,7 @@ class SyncBackendHost : public browser_sync::ModelSafeWorkerRegistrar {
   // Create a SyncBackendHost with a reference to the |frontend| that it serves
   // and communicates to via the SyncFrontend interface (on the same thread
   // it used to call the constructor).
-  SyncBackendHost(SyncFrontend* frontend, Profile* profile);
+  explicit SyncBackendHost(Profile* profile);
   // For testing.
   // TODO(skrul): Extract an interface so this is not needed.
   SyncBackendHost();
@@ -117,7 +117,8 @@ class SyncBackendHost : public browser_sync::ModelSafeWorkerRegistrar {
   // As a fallback when no cached auth information is available, try to
   // bootstrap authentication using |lsid|, if it isn't empty.
   // Optionally delete the Sync Data folder (if it's corrupt).
-  void Initialize(const GURL& service_url,
+  void Initialize(SyncFrontend* frontend,
+                  const GURL& service_url,
                   const syncable::ModelTypeSet& types,
                   URLRequestContextGetter* baseline_context_getter,
                   const sync_api::SyncCredentials& credentials,