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

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>
 #include <unordered_map>
 #include <vector>
 
 #include "base/optional.h"
+#include "content/public/common/web_preferences.h"
 #include "headless/public/headless_export.h"
 #include "headless/public/headless_web_contents.h"
 #include "net/base/host_port_pair.h"
 #include "net/url_request/url_request_job_factory.h"
 
 namespace base {
 class FilePath;
 }
 
 namespace headless {
 class HeadlessBrowserImpl;
 class HeadlessBrowserContextOptions;
 
+// Imported into headless namespace for
+// Builder::SetOverrideWebPreferencesCallback().
+using content::WebPreferences;
+
 using ProtocolHandlerMap = std::unordered_map<
     std::string,
     std::unique_ptr<net::URLRequestJobFactory::ProtocolHandler>>;
 
 // Represents an isolated session with a unique cache, cookies, and other
 // profile/session related data.
 // When browser context is deleted, all associated web contents are closed.
 class HEADLESS_EXPORT HeadlessBrowserContext {
  public:
   class Builder;
@@ skipping 52 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.

[Sami, 2016/09/29 09:38:26]

This is called on the browser main thread, right? And possibly multiple times?

[Eric Seckler, 2016/09/30 09:17:50]

It's definitely called multiple times (whenever the prefs of a RenderView
change). It looks like OverrideWebkitPrefs is executed on the browser main
thread and you don't have to worry about it being called by different threads,
but I also can't find anything explicitly confirming this.

Added a comment to these effects.

+  //
+  // WARNING: We cannot provide any guarantees about the stability of the
+  // exposed WebPreferences API, so use with care.
+  Builder& SetOverrideWebPreferencesCallback(
+      std::function<void(WebPreferences*)> callback);

[Sami, 2016/09/29 09:38:26]

This should probably be a base::Callback since most of Chrome is still built
that way.

[Eric Seckler, 2016/09/30 09:17:50]

Done.

+
   // 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);
 
@@ skipping 22 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_