Convert --{enable,disable}-simplified-fullscreen-ui to a feature flag.

chrome/browser/ui/exclusive_access/exclusive_access_manager.h

Index: chrome/browser/ui/exclusive_access/exclusive_access_manager.h
diff --git a/chrome/browser/ui/exclusive_access/exclusive_access_manager.h b/chrome/browser/ui/exclusive_access/exclusive_access_manager.h
index 68d7a5a6c3eb3c53ecaf0b2e4c66f162092e5af4..0a91afe647a324b5b3b048ca56d1e284ea7d6f14 100644
--- a/chrome/browser/ui/exclusive_access/exclusive_access_manager.h
+++ b/chrome/browser/ui/exclusive_access/exclusive_access_manager.h
@@ -5,6 +5,7 @@
 #ifndef CHROME_BROWSER_UI_EXCLUSIVE_ACCESS_EXCLUSIVE_ACCESS_MANAGER_H_
 #define CHROME_BROWSER_UI_EXCLUSIVE_ACCESS_EXCLUSIVE_ACCESS_MANAGER_H_
 
+#include "base/feature_list.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/ui/exclusive_access/exclusive_access_bubble_type.h"
@@ -26,6 +27,10 @@ class WebContents;
 // the exit bubble to reflect the combined state.
 class ExclusiveAccessManager {
  public:
+  // A new user experience for transitioning into fullscreen and mouse pointer
+  // lock states.
+  static const base::Feature kSimplifiedUIFeature;
+
   explicit ExclusiveAccessManager(
       ExclusiveAccessContext* exclusive_access_context);
   ~ExclusiveAccessManager();