Implement window management devtools commands for headless.

headless/test/headless_browser_test.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_TEST_HEADLESS_BROWSER_TEST_H_
 #define HEADLESS_TEST_HEADLESS_BROWSER_TEST_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 115 matching lines @@
   // Selects between creating the TabSocket only in an isolated world or the
   // main world.
   virtual bool GetCreateTabSocketOnlyForIsolatedWorld();
 
  protected:
   void RunTest();
 
   HeadlessBrowserContext* browser_context_;  // Not owned.
   HeadlessWebContents* web_contents_;
   std::unique_ptr<HeadlessDevToolsClient> devtools_client_;
+  std::unique_ptr<HeadlessDevToolsClient> browser_devtools_client_;
   bool render_process_exited_;
 };
 
 }  // namespace headless
 
 #endif  // HEADLESS_TEST_HEADLESS_BROWSER_TEST_H_