Convert enable_one_click_signin to new buildflag system

chrome/browser/ui/views/frame/browser_view.cc

Index: chrome/browser/ui/views/frame/browser_view.cc
diff --git a/chrome/browser/ui/views/frame/browser_view.cc b/chrome/browser/ui/views/frame/browser_view.cc
index 8f1096b93c9fb9148e9677497ab3e32163a9aba2..2edae31c9bd16dcf71b9fbeb9b5191e72fbfeb29 100644
--- a/chrome/browser/ui/views/frame/browser_view.cc
+++ b/chrome/browser/ui/views/frame/browser_view.cc
@@ -101,6 +101,7 @@
 #include "chrome/browser/ui/window_sizer/window_sizer.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/extensions/command.h"
+#include "chrome/common/features.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/grit/chromium_strings.h"
@@ -172,7 +173,7 @@
 #include "ui/views/win/scoped_fullscreen_visibility.h"
 #endif
 
-#if defined(ENABLE_ONE_CLICK_SIGNIN)
+#if BUILDFLAG(ENABLE_ONE_CLICK_SIGNIN)
 #include "chrome/browser/ui/sync/one_click_signin_bubble_delegate.h"
 #include "chrome/browser/ui/sync/one_click_signin_bubble_links_delegate.h"
 #include "chrome/browser/ui/views/sync/one_click_signin_bubble_view.h"
@@ -1337,7 +1338,7 @@ void BrowserView::ShowTranslateBubble(
   GetToolbarView()->OnBubbleCreatedForAnchor(anchor_view, bubble_widget);
 }
 
-#if defined(ENABLE_ONE_CLICK_SIGNIN)
+#if BUILDFLAG(ENABLE_ONE_CLICK_SIGNIN)
 void BrowserView::ShowOneClickSigninBubble(
     OneClickSigninBubbleType type,
     const base::string16& email,