[content shell] use the TestRunner library's theme engine for layout tests

content/shell/shell_content_renderer_client.cc

Index: content/shell/shell_content_renderer_client.cc
diff --git a/content/shell/shell_content_renderer_client.cc b/content/shell/shell_content_renderer_client.cc
index 3de69420c10c068a1e41d50b68c03bcca2aeab3c..e794f0d8c20a0a08322d73508db120f4a67d83a0 100644
--- a/content/shell/shell_content_renderer_client.cc
+++ b/content/shell/shell_content_renderer_client.cc
@@ -157,9 +157,8 @@ WebHyphenator* ShellContentRendererClient::OverrideWebHyphenator() {
 WebThemeEngine* ShellContentRendererClient::OverrideThemeEngine() {
   if (!CommandLine::ForCurrentProcess()->HasSwitch(switches::kDumpRenderTree))
     return NULL;
-  // TODO(jochen): return the TestRunner library's theme engine once WebKit has
-  // rolled.
-  return NULL;
+  return ShellRenderProcessObserver::GetInstance()->test_interfaces()
+      ->themeEngine();
 }
 
 void ShellContentRendererClient::WebTestProxyCreated(RenderView* render_view,