Remove unused |context| from GetDefaultParent().

ui/aura/test/test_window_parenting_client.h

 // Copyright (c) 2013 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 UI_AURA_TEST_TEST_WINDOW_PARENTING_CLIENT_H_
 #define UI_AURA_TEST_TEST_WINDOW_PARENTING_CLIENT_H_
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "ui/aura/aura_export.h"
 #include "ui/aura/client/window_parenting_client.h"
 
 namespace aura {
 namespace test {
 
 class TestWindowParentingClient : public client::WindowParentingClient {
  public:
   explicit TestWindowParentingClient(Window* root_window);
   ~TestWindowParentingClient() override;
 
   // Overridden from client::WindowParentingClient:
-  Window* GetDefaultParent(Window* context,
-                           Window* window,
-                           const gfx::Rect& bounds) override;
+  Window* GetDefaultParent(Window* window, const gfx::Rect& bounds) override;
 
  private:
   Window* root_window_;
 
   DISALLOW_COPY_AND_ASSIGN(TestWindowParentingClient);
 };
 
 }  // namespace test
 }  // namespace aura
 
 #endif  // UI_AURA_TEST_TEST_WINDOW_PARENTING_CLIENT_H_