PlzNavigate: properly execute BeforeUnload on renderer initiated navigations

third_party/WebKit/public/web/WebLocalFrame.h

Index: third_party/WebKit/public/web/WebLocalFrame.h
diff --git a/third_party/WebKit/public/web/WebLocalFrame.h b/third_party/WebKit/public/web/WebLocalFrame.h
index 7dd32559f963276187c6abdf5c307cec2696d570..8b36857246f23750ff60b9615b241b04ca12bfb8 100644
--- a/third_party/WebKit/public/web/WebLocalFrame.h
+++ b/third_party/WebKit/public/web/WebLocalFrame.h
@@ -86,6 +86,11 @@ public:
 
     // Navigation ----------------------------------------------------------
 
+    // Runs beforeunload handlers for this frame and updates |proceed| with the
+    // value returned by handlers. Returns false if the execution of
+    // BeforeUnload led to the destruction of the frame, true otherwise.
+    virtual bool dispatchBeforeUnloadEvent(bool* proceed) = 0;

[dcheng, 2016/05/03 06:51:59]

Rather than using a bool out param, I'd suggest just combining the meanings into
the return val.

return false => don't navigate, bail out immediately, frame might be destroyed
return true => ok to proceed

Alternatively, we can express the state with an enum, which might make the code
clearer but isn't really needed atm.

[clamy, 2016/05/03 13:17:09]

There is one case where we need to distinguish between the two: cross-site
navigations where the browser expect an IPC back with the return value of
BeforeUnload. So I went with the enum option.

+
     // Returns a WebURLRequest corresponding to the load of the WebHistoryItem.
     virtual WebURLRequest requestFromHistoryItem(const WebHistoryItem&, WebCachePolicy) const = 0;