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

headless/lib/browser/headless_content_browser_client.cc

Index: headless/lib/browser/headless_content_browser_client.cc
diff --git a/headless/lib/browser/headless_content_browser_client.cc b/headless/lib/browser/headless_content_browser_client.cc
index 9f36dec6fa2cd9f03d3f507d183337ecb878e2d8..7cdef1db10600daa7d3a015bfe1a196fa61adb7b 100644
--- a/headless/lib/browser/headless_content_browser_client.cc
+++ b/headless/lib/browser/headless_content_browser_client.cc
@@ -7,7 +7,11 @@
 #include <memory>
 
 #include "base/memory/ptr_util.h"
+#include "content/public/browser/browser_context.h"
 #include "content/public/browser/browser_thread.h"
+#include "content/public/browser/render_process_host.h"
+#include "content/public/browser/render_view_host.h"
+#include "headless/lib/browser/headless_browser_context_impl.h"
 #include "headless/lib/browser/headless_browser_impl.h"
 #include "headless/lib/browser/headless_browser_main_parts.h"
 #include "headless/lib/browser/headless_devtools_manager_delegate.h"
@@ -28,6 +32,17 @@ content::BrowserMainParts* HeadlessContentBrowserClient::CreateBrowserMainParts(
   return browser_main_parts.release();
 }
 
+void HeadlessContentBrowserClient::OverrideWebkitPrefs(
+    content::RenderViewHost* render_view_host,
+    content::WebPreferences* prefs) {
+  auto browser_context = HeadlessBrowserContextImpl::From(
+      render_view_host->GetProcess()->GetBrowserContext());
+  const std::function<void(headless::WebPreferences*)>& callback =
+      browser_context->options()->override_web_preferences_callback();
+  if (callback)
+    callback(prefs);
+}
+
 content::DevToolsManagerDelegate*
 HeadlessContentBrowserClient::GetDevToolsManagerDelegate() {
   return new HeadlessDevToolsManagerDelegate(browser_->GetWeakPtr());