Exclude building signin view controller and its delegate on ChromeOS

chrome/browser/ui/signin_view_controller.h

Index: chrome/browser/ui/signin_view_controller.h
diff --git a/chrome/browser/ui/signin_view_controller.h b/chrome/browser/ui/signin_view_controller.h
index adc7ce5825d65d4b9b83411382ff6e2de40703c2..9a45e84956d9e517f1ab90ea90f11b7e00a51a29 100644
--- a/chrome/browser/ui/signin_view_controller.h
+++ b/chrome/browser/ui/signin_view_controller.h
@@ -17,6 +17,9 @@ 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();