Remove unused |context| from GetDefaultParent().

headless/lib/browser/headless_window_parenting_client.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 HEADLESS_LIB_BROWSER_HEADLESS_WINDOW_PARENTING_CLIENT_H_
 #define HEADLESS_LIB_BROWSER_HEADLESS_WINDOW_PARENTING_CLIENT_H_
 
 #include "base/macros.h"
 #include "ui/aura/client/window_parenting_client.h"
 
 namespace headless {
 
 class HeadlessWindowParentingClient
     : public aura::client::WindowParentingClient {
  public:
   explicit HeadlessWindowParentingClient(aura::Window* root_window);
   ~HeadlessWindowParentingClient() override;
 
-  aura::Window* GetDefaultParent(aura::Window* context,
-                                 aura::Window* window,
+  aura::Window* GetDefaultParent(aura::Window* window,
                                  const gfx::Rect& bounds) override;
 
  private:
   aura::Window* root_window_;  // Not owned.
 
   DISALLOW_COPY_AND_ASSIGN(HeadlessWindowParentingClient);
 };
 
 }  // namespace headless
 
 #endif  // HEADLESS_LIB_BROWSER_HEADLESS_WINDOW_PARENTING_CLIENT_H_