Pipe the devTools FrameId from blink into the browser for headless

content/public/browser/devtools_agent_host.h

Index: content/public/browser/devtools_agent_host.h
diff --git a/content/public/browser/devtools_agent_host.h b/content/public/browser/devtools_agent_host.h
index 15fd91c3906b64fc510a4d4f2bc01a972cfdd3e7..3e49eafcb3bfbdf55607abdb4faf74bfa7fa5150 100644
--- a/content/public/browser/devtools_agent_host.h
+++ b/content/public/browser/devtools_agent_host.h
@@ -52,6 +52,10 @@ class CONTENT_EXPORT DevToolsAgentHost
   // Returns whether particular version of DevTools protocol is supported.
   static bool IsSupportedProtocolVersion(const std::string& version);
 
+  // Returns the DevTools FrameId for the given |frame_tree_node_id|.
+  static std::string GetDevToolsFrameIdForFrameTreeNodeId(
+      int frame_tree_node_id);
+
   // Returns DevToolsAgentHost with a given |id| or nullptr of it doesn't exist.
   static scoped_refptr<DevToolsAgentHost> GetForId(const std::string& id);