Allow override of user agent depending on url.

content/renderer/render_frame_impl.cc

Index: content/renderer/render_frame_impl.cc
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
index ca5cf55aa3761765972eae6c626116de02aeba1e..426474ba8d3395e031e88f71754cdf36d9f42598 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -3129,6 +3129,16 @@ bool RenderFrameImpl::willCheckAndDispatchMessageEvent(
 blink::WebString RenderFrameImpl::userAgentOverride(blink::WebLocalFrame* frame,
                                                     const blink::WebURL& url) {
   DCHECK(!frame_ || frame_ == frame);
+
+  ObserverListBase<RenderFrameObserver>::Iterator it(observers_);
+  RenderFrameObserver* observer;
+  while ((observer = it.GetNext()) != NULL) {
+    std::string user_agent_override_for_url =
+        observer->GetUserAgentOverrideForURL(GURL(url));
+    if (!user_agent_override_for_url.empty())
+      return WebString::fromUTF8(user_agent_override_for_url);
+  }
+
   if (!render_view_->webview() || !render_view_->webview()->mainFrame() ||
       render_view_->renderer_preferences_.user_agent_override.empty()) {
     return blink::WebString();