Pipe the devTools FrameId from blink into the browser for headless

headless/public/headless_web_contents.h

Index: headless/public/headless_web_contents.h
diff --git a/headless/public/headless_web_contents.h b/headless/public/headless_web_contents.h
index 93f6262eda0c89311ac95067abef21e5f2a66e26..8986358bdb80bdb68a95936416b6dcddc98a8a78 100644
--- a/headless/public/headless_web_contents.h
+++ b/headless/public/headless_web_contents.h
@@ -83,8 +83,9 @@ class HEADLESS_EXPORT HeadlessWebContents {
   // Returns the headless tab socket for JS -> C++ if one was created.
   virtual HeadlessTabSocket* GetHeadlessTabSocket() const = 0;
 
-  // Returns the frame tree node id associated with the |devtools_agent_host_id|
+  // Returns the FrameTreeNode Id associated with the |devtools_agent_host_id|
   // if any.
+  // TODO(alexclarke): Remove this, it doesn't work as expected.
   virtual bool GetFrameTreeNodeIdForDevToolsAgentHostId(
       const std::string& devtools_agent_host_id,
       int* frame_tree_node_id) const = 0;