Cleanup: Remove unneeded extension_messages.h usage and ifdef out some extensions code usage when e…

chrome/browser/sessions/session_tab_helper.h

 // Copyright (c) 2011 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 CHROME_BROWSER_SESSIONS_SESSION_TAB_HELPER_H_
 #define CHROME_BROWSER_SESSIONS_SESSION_TAB_HELPER_H_
 
 #include "base/basictypes.h"
 #include "components/sessions/session_id.h"
 #include "content/public/browser/web_contents_observer.h"
@@ skipping 25 matching lines @@
   // window, returns Browser::session_id().id() for that Browser. If the tab is
   // being dragged between Browser windows, returns the old window's id value.
   // If the WebContents has a SessionTabHelper but has never been attached to a
   // Browser window, returns an id value that is different from that of any
   // Browser. Returns -1 for a NULL WebContents or if the WebContents has no
   // SessionTabHelper.
   static SessionID::id_type IdForWindowContainingTab(
       const content::WebContents* tab);
 
   // content::WebContentsObserver:
+#if defined(ENABLE_EXTENSIONS)

[Yoyo Zhou, 2014/09/18 20:34:02]

nit: you could just ifdef out the implementation, which saves you having to
ifdef the function definition here. Not sure if that's worth it.

[Lei Zhang, 2014/09/18 21:31:56]

If I ifdef out the impl, but not the method decl here, then the linker will
complain.

[Yoyo Zhou, 2014/09/18 21:41:13]

Not the whole impl. The #ifdef could be inside the function braces.

   virtual void RenderViewCreated(
       content::RenderViewHost* render_view_host) OVERRIDE;
+#endif
   virtual void UserAgentOverrideSet(const std::string& user_agent) OVERRIDE;
 
  private:
   explicit SessionTabHelper(content::WebContents* contents);
   friend class content::WebContentsUserData<SessionTabHelper>;
 
   // Unique identifier of the tab for session restore. This id is only unique
   // within the current session, and is not guaranteed to be unique across
   // sessions.
   const SessionID session_id_;
 
   // Unique identifier of the window the tab is in.
   SessionID window_id_;
 
   DISALLOW_COPY_AND_ASSIGN(SessionTabHelper);
 };
 
 #endif  // CHROME_BROWSER_SESSIONS_SESSION_TAB_HELPER_H_