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

headless/lib/browser/headless_browser_context_options.cc

Index: headless/lib/browser/headless_browser_context_options.cc
diff --git a/headless/lib/browser/headless_browser_context_options.cc b/headless/lib/browser/headless_browser_context_options.cc
index 13faa83889e3f8d6b69ab4f63af06e23b926e95c..2dd7939e26af2e08ecdd0f97753bfb2d8ea42744 100644
--- a/headless/lib/browser/headless_browser_context_options.cc
+++ b/headless/lib/browser/headless_browser_context_options.cc
@@ -61,6 +61,13 @@ bool HeadlessBrowserContextOptions::incognito_mode() const {
                                browser_options_->incognito_mode);
 }
 
+const base::Callback<void(WebPreferences*)>&
+HeadlessBrowserContextOptions::override_web_preferences_callback() const {
+  return ReturnOverriddenValue(
+      override_web_preferences_callback_,
+      browser_options_->override_web_preferences_callback);
+}
+
 const ProtocolHandlerMap& HeadlessBrowserContextOptions::protocol_handlers()
     const {
   return protocol_handlers_;
@@ -70,9 +77,4 @@ ProtocolHandlerMap HeadlessBrowserContextOptions::TakeProtocolHandlers() {
   return std::move(protocol_handlers_);
 }
 
-const base::Callback<void(WebPreferences*)>&
-HeadlessBrowserContextOptions::override_web_preferences_callback() const {
-  return override_web_preferences_callback_;
-}
-
 }  // namespace headless