[Sync] Return nullptr for OpenTabsUIDelegate when PROXY_TABS is disabled.

components/sync/driver/sync_service.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // 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_SERVICE_H_
 #define COMPONENTS_SYNC_DRIVER_SYNC_SERVICE_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 187 matching lines @@
   virtual bool ConfigurationDone() const = 0;
 
   virtual const GoogleServiceAuthError& GetAuthError() const = 0;
   virtual bool HasUnrecoverableError() const = 0;
 
   // Returns true if the SyncBackendHost has told us it's ready to accept
   // changes. This should only be used for sync's internal configuration logic
   // (such as deciding when to prompt for an encryption passphrase).
   virtual bool IsBackendInitialized() const = 0;
 
-  // Return the active OpenTabsUIDelegate. If sessions is not enabled or not
-  // currently syncing, returns nullptr.
+  // Return the active OpenTabsUIDelegate. If open/proxy tabs is not enabled or
+  // not currently syncing, returns nullptr.
   virtual sync_sessions::OpenTabsUIDelegate* GetOpenTabsUIDelegate() = 0;
 
   // Returns true if OnPassphraseRequired has been called for decryption and
   // we have an encrypted data type enabled.
   virtual bool IsPassphraseRequiredForDecryption() const = 0;
 
   // Returns the time the current explicit passphrase (if any), was set.
   // If no secondary passphrase is in use, or no time is available, returns an
   // unset base::Time.
   virtual base::Time GetExplicitPassphraseTime() const = 0;
@@ skipping 108 matching lines @@
  protected:
   SyncService() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SyncService);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_DRIVER_SYNC_SERVICE_H_