Headless: expose WebPreferences to embedder, add --hide-scrollbars.

headless/lib/browser/headless_content_browser_client.h

 // Copyright 2015 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_CONTENT_BROWSER_CLIENT_H_
 #define HEADLESS_LIB_BROWSER_HEADLESS_CONTENT_BROWSER_CLIENT_H_
 
 #include "content/public/browser/content_browser_client.h"
 
 namespace headless {
 
 class HeadlessBrowserImpl;
 class HeadlessBrowserMainParts;
 class HeadlessDevToolsManagerDelegate;
 
 class HeadlessContentBrowserClient : public content::ContentBrowserClient {
  public:
   explicit HeadlessContentBrowserClient(HeadlessBrowserImpl* browser);
   ~HeadlessContentBrowserClient() override;
 
   // content::ContentBrowserClient implementation:
   content::BrowserMainParts* CreateBrowserMainParts(
       const content::MainFunctionParams&) override;
-
+  void OverrideWebkitPrefs(content::RenderViewHost* render_view_host,
+                           content::WebPreferences* prefs) override;
   content::DevToolsManagerDelegate* GetDevToolsManagerDelegate() override;
 
  private:
   HeadlessBrowserImpl* browser_;  // Not owned.
 
   DISALLOW_COPY_AND_ASSIGN(HeadlessContentBrowserClient);
 };
 
 }  // namespace headless
 
 #endif  // HEADLESS_LIB_BROWSER_HEADLESS_CONTENT_BROWSER_CLIENT_H_