Skip BeforeUnload on cross-site navigations when there are no handlers

content/browser/frame_host/render_frame_host_impl.cc

Index: content/browser/frame_host/render_frame_host_impl.cc
diff --git a/content/browser/frame_host/render_frame_host_impl.cc b/content/browser/frame_host/render_frame_host_impl.cc
index e6cc05197d3a25613468d2938787f3f54da90757..821be812fce862c4134dec1cc90155f2b13bae1d 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -920,6 +920,9 @@ void RenderFrameHostImpl::SwapOut(
     replication_state = proxy->frame_tree_node()->current_replication_state();
   }
 
+  // TODO(clamy): if the frame has no unload handlers and |proxy| is null, it
+  // could be discarded immediately, improving performance. However that means
+  // losing the last sync of PageState.
   if (IsRenderFrameLive()) {
     Send(new FrameMsg_SwapOut(routing_id_, proxy_routing_id, is_loading,
                               replication_state));
@@ -1551,10 +1554,17 @@ void RenderFrameHostImpl::Stop() {
 }
 
 void RenderFrameHostImpl::DispatchBeforeUnload(bool for_navigation) {
-  // TODO(creis): Support beforeunload on subframes.  For now just pretend that
+  // Skip running beforeUnload if:
+  //   - the renderer is not live.
+  //   - the frame is a subframe.
+  //   - this is a cross-site navigation and the current frame has no
+  //   beforeUnload handler registered.
+  // TODO(creis): Support beforeUnload on subframes.  For now just pretend that
   // the handler ran and allowed the navigation to proceed.
-  if (GetParent() || !IsRenderFrameLive()) {
-    // We don't have a live renderer, so just skip running beforeunload.
+  // TODO(clamy): Skip beforeUnload when closing a frame with no registered
+  // beforeUnload handlers.
+  if (GetParent() || !IsRenderFrameLive() ||
+      (!has_beforeunload_handlers_ && for_navigation)) {
     if (base::CommandLine::ForCurrentProcess()->HasSwitch(
         switches::kEnableBrowserSideNavigation)) {
       frame_tree_node_->navigator()->OnBeforeUnloadACK(