Don't reset LoadEventProgress if frame unload has already started.

third_party/WebKit/Source/core/loader/FrameLoader.cpp

Index: third_party/WebKit/Source/core/loader/FrameLoader.cpp
diff --git a/third_party/WebKit/Source/core/loader/FrameLoader.cpp b/third_party/WebKit/Source/core/loader/FrameLoader.cpp
index 27cc4b93872c298865140447341d021f73a9bb7a..cd59f695f15c80487e07b3f64008bea19f1da635 100644
--- a/third_party/WebKit/Source/core/loader/FrameLoader.cpp
+++ b/third_party/WebKit/Source/core/loader/FrameLoader.cpp
@@ -1042,6 +1042,9 @@ bool FrameLoader::prepareForCommit()
         ThreadState::current()->schedulePageNavigationGCIfNeeded(ratio);
     }
 
+    // TODO(dcheng): See comment in LocalFrame::detach() about sequencing this
+    // immediately before detachChildren() instead.
+    SubframeLoadingDisabler disabler(m_frame->document());

[dcheng, 2016/02/03 08:42:17]

Here, m_frame->document() might be null during the commit of the initial empty
page.

The other alternative was to make SubframeLoadingDisabler not stack allocated,
but that gets complicated as well.

     if (m_documentLoader) {
         client()->dispatchWillClose();
         dispatchUnloadEvent();