PlzNavigate: Speculatively spawns a renderer process for navigations.

content/browser/frame_host/navigator_impl.cc

Index: content/browser/frame_host/navigator_impl.cc
diff --git a/content/browser/frame_host/navigator_impl.cc b/content/browser/frame_host/navigator_impl.cc
index e3b56215d4d26daf3218f1b52f0133bda53ffdc0..b62feaf3bb32f79ad854f4779adcfdd64ff6f4d3 100644
--- a/content/browser/frame_host/navigator_impl.cc
+++ b/content/browser/frame_host/navigator_impl.cc
@@ -738,10 +738,9 @@ void NavigatorImpl::OnBeginNavigation(
   info->parent_is_main_frame = !frame_tree_node->parent() ?
       false : frame_tree_node->parent()->IsMainFrame();
 
-  // TODO(clamy): Inform the RenderFrameHostManager that a navigation is about
-  // to begin, so that it can speculatively spawn a new renderer if needed.
-
   navigation_request->BeginNavigation(info.Pass(), params.request_body);
+
+  frame_tree_node->render_manager()->BeginNavigation(params, common_params);
 }
 
 // PlzNavigate
@@ -782,6 +781,7 @@ void NavigatorImpl::CancelNavigation(FrameTreeNode* frame_tree_node) {
   CHECK(CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kEnableBrowserSideNavigation));
   navigation_request_map_.erase(frame_tree_node->frame_tree_node_id());
+  frame_tree_node->render_manager()->CancelNavigation();
 }
 
 void NavigatorImpl::LogResourceRequestTime(