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

headless/app/headless_shell.cc

 // 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.
 
 #include <memory>
 #include <sstream>
 #include <string>
 
 #include "base/base64.h"
 #include "base/bind.h"
@@ skipping 74 matching lines @@
       ProtocolHandlerMap protocol_handlers;
       protocol_handlers[url::kHttpScheme] =
           base::MakeUnique<DeterministicHttpProtocolHandler>(
               deterministic_dispatcher_.get(), browser->BrowserIOThread());
       protocol_handlers[url::kHttpsScheme] =
           base::MakeUnique<DeterministicHttpProtocolHandler>(
               deterministic_dispatcher_.get(), browser->BrowserIOThread());
 
       context_builder.SetProtocolHandlers(std::move(protocol_handlers));
     }
-    if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-            switches::kHideScrollbars)) {
-      context_builder.SetOverrideWebPreferencesCallback(
-          base::Bind([](WebPreferences* preferences) {
-            preferences->hide_scrollbars = true;
-          }));
-    }
     browser_context_ = context_builder.Build();
     browser_->SetDefaultBrowserContext(browser_context_);
 
     HeadlessWebContents::Builder builder(
         browser_context_->CreateWebContentsBuilder());
     base::CommandLine::StringVector args =
         base::CommandLine::ForCurrentProcess()->GetArgs();
 
     // TODO(alexclarke): Should we navigate to about:blank first if using
     // virtual time?
@@ skipping 399 matching lines @@
     std::string window_size =
         command_line.GetSwitchValueASCII(switches::kWindowSize);
     gfx::Size parsed_window_size;
     if (!ParseWindowSize(window_size, &parsed_window_size)) {
       LOG(ERROR) << "Malformed window size";
       return EXIT_FAILURE;
     }
     builder.SetWindowSize(parsed_window_size);
   }
 
+  if (command_line.HasSwitch(switches::kHideScrollbars)) {
+    builder.SetOverrideWebPreferencesCallback(base::Bind([](
+        WebPreferences* preferences) { preferences->hide_scrollbars = true; }));
+  }
+
   return HeadlessBrowserMain(
       builder.Build(),
       base::Bind(&HeadlessShell::OnStart, base::Unretained(&shell)));
 }
 
 }  // namespace headless