[headless] Make --hide-scrollbars affect all BrowserContexts.

headless/public/headless_browser_context.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_PUBLIC_HEADLESS_BROWSER_CONTEXT_H_
 #define HEADLESS_PUBLIC_HEADLESS_BROWSER_CONTEXT_H_
 
 #include <list>
 #include <memory>
 #include <string>
@@ skipping 85 matching lines @@
   // access to these bindings.  If you know what you're doing it may be OK to
   // turn them back on. E.g. if headless_lib is being used in a testing
   // framework which serves the web content from disk that's likely ok.
   //
   // That said, best pratice is to add a ProtocolHandler to serve the
   // webcontent over a custom protocol. That way you can be sure that only the
   // things you intend have access to mojo.
   Builder& EnableUnsafeNetworkAccessWithMojoBindings(
       bool enable_http_and_https_if_mojo_used);
 
-  // Set a callback that is invoked to override WebPreferences for RenderViews
-  // created within this HeadlessBrowserContext. Called whenever the
-  // WebPreferences of a RenderView change. Executed on the browser main thread.
-  //
-  // WARNING: We cannot provide any guarantees about the stability of the
-  // exposed WebPreferences API, so use with care.
-  Builder& SetOverrideWebPreferencesCallback(
-      base::Callback<void(WebPreferences*)> callback);
-
   // By default |HeadlessBrowserContext| inherits the following options from
   // the browser instance. The methods below can be used to override these
   // settings. See HeadlessBrowser::Options for their meaning.
   Builder& SetUserAgent(const std::string& user_agent);
   Builder& SetProxyServer(const net::HostPortPair& proxy_server);
   Builder& SetHostResolverRules(const std::string& host_resolver_rules);
   Builder& SetWindowSize(const gfx::Size& window_size);
   Builder& SetUserDataDir(const base::FilePath& user_data_dir);
   Builder& SetIncognitoMode(bool incognito_mode);
+  Builder& SetOverrideWebPreferencesCallback(
+      base::Callback<void(WebPreferences*)> callback);
 
   HeadlessBrowserContext* Build();
 
  private:
   friend class HeadlessBrowserImpl;
   friend class HeadlessBrowserContextImpl;
 
   explicit Builder(HeadlessBrowserImpl* browser);
 
   struct MojoBindings {
@@ skipping 13 matching lines @@
 
   std::list<MojoBindings> mojo_bindings_;
   bool enable_http_and_https_if_mojo_used_;
 
   DISALLOW_COPY_AND_ASSIGN(Builder);
 };
 
 }  // namespace headless
 
 #endif  // HEADLESS_PUBLIC_HEADLESS_BROWSER_CONTEXT_H_