PlzNavigate: Get StreamPrivate API to work.

content/browser/web_contents/web_contents_impl.cc

Index: content/browser/web_contents/web_contents_impl.cc
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index 10187d104037ca97078b9e33ddeca6b6f2b2886f..b4379ca1b4da6085d77539d2f25d366ca1d1ec93 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -44,6 +44,7 @@
 #include "content/browser/download/save_package.h"
 #include "content/browser/find_request_manager.h"
 #include "content/browser/frame_host/cross_process_frame_connector.h"
+#include "content/browser/frame_host/frame_tree_node.h"
 #include "content/browser/frame_host/interstitial_page_impl.h"
 #include "content/browser/frame_host/navigation_entry_impl.h"
 #include "content/browser/frame_host/navigation_handle_impl.h"
@@ -302,6 +303,12 @@ WebContents* WebContents::FromRenderFrameHost(RenderFrameHost* rfh) {
   return static_cast<RenderFrameHostImpl*>(rfh)->delegate()->GetAsWebContents();
 }
 
+WebContents* WebContents::FromFrameTreeNodeId(int frame_tree_node_id) {
+  FrameTreeNode* frame_tree_node =
+      FrameTreeNode::GloballyFindByID(frame_tree_node_id);
+  return FromRenderFrameHost(frame_tree_node->current_frame_host());
+}
+
 // WebContentsImpl::DestructionObserver ----------------------------------------
 
 class WebContentsImpl::DestructionObserver : public WebContentsObserver {