Keep track in the browser of which frames have onunload and onbeforeunload handlers.

content/browser/web_contents/web_contents_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/web_contents/web_contents_impl.h"
 
 #include <stddef.h>
 
 #include <cmath>
 #include <utility>
@@ skipping 1404 matching lines @@
 void WebContentsImpl::WasUnOccluded() {
   for (RenderWidgetHostView* view : GetRenderWidgetHostViewsInTree()) {
     if (view)
       view->WasUnOccluded();
   }
 }
 
 bool WebContentsImpl::NeedToFireBeforeUnload() {
   // TODO(creis): Should we fire even for interstitial pages?
   return WillNotifyDisconnection() && !ShowingInterstitialPage() &&
-         !GetRenderViewHost()->SuddenTerminationAllowed();
+         !GetRenderViewHost()->SuddenTerminationAllowed() &&
+         (GetMainFrame()->ShouldDispatchBeforeUnload() ||
+          GetMainFrame()->ShouldDispatchUnload());

[nasko, 2017/03/29 21:45:17]

Why would unload handler matter for NeedToFireBeforeUnload?

[jam, 2017/03/29 22:19:09]

That was my initial thought as well. I had to add the unload case to fix a few
tests (see patchset 6 -> 7. This fixed 
ExtensionApiTest.MessagingOnUnload
FastUnloadTest.UnloadHidden
PrerenderBrowserTest.PrerenderUnload 

It was because of how the UnloadController works today. It turns out that this
method's comments also specifically mention beforeunload and unload:
https://cs.chromium.org/chromium/src/content/public/browser/web_contents.h?rc...
"Returns true if the before unload and unload listeners need to fired."

 }
 
 void WebContentsImpl::DispatchBeforeUnload() {
   bool for_cross_site_transition = false;
   GetMainFrame()->DispatchBeforeUnload(for_cross_site_transition, false);
 }
 
 void WebContentsImpl::AttachToOuterWebContentsFrame(
     WebContents* outer_web_contents,
     RenderFrameHost* outer_contents_frame) {
@@ skipping 3975 matching lines @@
     RenderViewHost* render_view_host = RenderViewHost::From(render_widget_host);
     if (!render_view_host)
       continue;
     render_view_host_set.insert(render_view_host);
   }
   for (RenderViewHost* render_view_host : render_view_host_set)
     render_view_host->OnWebkitPreferencesChanged();
 }
 
 }  // namespace content