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

headless/public/headless_browser.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_PUBLIC_HEADLESS_BROWSER_H_
 #define HEADLESS_PUBLIC_HEADLESS_BROWSER_H_
 
 #include <memory>
 #include <string>
 #include <unordered_map>
@@ skipping 131 matching lines @@
   // as initial screen size. Defaults to 800x600.
   gfx::Size window_size;
 
   // Path to user data directory, where browser will look for its state.
   // If empty, default directory (where the binary is located) will be used.
   base::FilePath user_data_dir;
 
   // Run a browser context in an incognito mode. Enabled by default.
   bool incognito_mode;
 
+  // Set a callback that is invoked to override WebPreferences for RenderViews
+  // created within the HeadlessBrowser. 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.
+  base::Callback<void(WebPreferences*)> override_web_preferences_callback;
+
   // Reminder: when adding a new field here, do not forget to add it to
   // HeadlessBrowserContextOptions (where appropriate).
  private:
   Options(int argc, const char** argv);
 
   DISALLOW_COPY_AND_ASSIGN(Options);
 };
 
 class HeadlessBrowser::Options::Builder {
  public:
@@ skipping 11 matching lines @@
   Builder& AddMojoServiceName(const std::string& mojo_service_name);
 
   // Per-context settings.
 
   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);
 
   Options Build();
 
  private:
   Options options_;
 
   DISALLOW_COPY_AND_ASSIGN(Builder);
 };
 
 // The headless browser may need to create child processes (e.g., a renderer
@@ skipping 23 matching lines @@
 // the main loop, it will only return after HeadlessBrowser::Shutdown() is
 // called, returning the exit code for the process. It is not possible to
 // initialize the browser again after it has been torn down.
 int HeadlessBrowserMain(
     HeadlessBrowser::Options options,
     const base::Callback<void(HeadlessBrowser*)>& on_browser_start_callback);
 
 }  // namespace headless
 
 #endif  // HEADLESS_PUBLIC_HEADLESS_BROWSER_H_