Exclude building signin view controller and its delegate on ChromeOS

chrome/browser/ui/signin_view_controller.h

 // Copyright 2016 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_UI_SIGNIN_VIEW_CONTROLLER_H_
 #define CHROME_BROWSER_UI_SIGNIN_VIEW_CONTROLLER_H_
 
 #include "base/macros.h"
 #include "chrome/browser/ui/profile_chooser_constants.h"
 
 class Browser;
 class SigninViewControllerDelegate;
 
 namespace signin_metrics {
 enum class AccessPoint;
 }
 
 // Class responsible for showing and hiding the Signin and Sync Confirmation
 // tab-modal dialogs.
+//
+// Note: This class only exists on Desktop platforms (it does not exist on
+// mobile or ChromeOS)

[Peter Kasting, 2017/03/29 19:39:31]

Nit: Since CrOS is a desktop platform, this is a bit confusing; just say "Note:
This class is not used on mobile or CrOS."

I'd say "not compiled in", but this is compiled in, in stub form, on CrOS after
this patch.  Is it feasible to make it not be compiled-in at all?  Can we have
like a #if USE_SIGNIN that guards access to this type, so it's obvious to
readers of calling code that said code is not always functional?  Maybe those
callers are already not compiled in on the target platforms?

[msarda, 2017/03/30 11:54:11]

I excluded this file on ChromeOS entirely and removed this comment.

 class SigninViewController {
  public:
   SigninViewController();
   virtual ~SigninViewController();
 
   // Returns true if the signin flow should be shown as tab-modal for |mode|.
   static bool ShouldShowModalSigninForMode(profiles::BubbleViewMode mode);
 
   // Shows the signin flow as a tab modal dialog attached to |browser|'s active
   // web contents.
@@ skipping 20 matching lines @@
     return signin_view_controller_delegate_;
   }
 
  private:
   SigninViewControllerDelegate* signin_view_controller_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(SigninViewController);
 };
 
 #endif  // CHROME_BROWSER_UI_SIGNIN_VIEW_CONTROLLER_H_