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..d9ff10255d983a431a82f8c790bd8bc9eefa8e78 100644
--- a/third_party/WebKit/Source/core/loader/FrameLoader.cpp
+++ b/third_party/WebKit/Source/core/loader/FrameLoader.cpp
@@ -329,6 +329,10 @@ void FrameLoader::replaceDocumentWhileExecutingJavaScriptURL(const String& sourc
     init.withNewRegistrationContext();
 
     stopAllLoaders();
+    // Don't allow any new child frames to load in this frame: attaching a new
+    // child frame during or after detaching children results in an attached
+    // frame on a detached DOM tree, which is bad.
+    SubframeLoadingDisabler disabler(m_frame->document());
     m_frame->detachChildren();
     m_frame->document()->detach();
     clear();
@@ -1042,6 +1046,10 @@ bool FrameLoader::prepareForCommit()
         ThreadState::current()->schedulePageNavigationGCIfNeeded(ratio);
     }
 
+    // Don't allow any new child frames to load in this frame: attaching a new
+    // child frame during or after detaching children results in an attached
+    // frame on a detached DOM tree, which is bad.
+    SubframeLoadingDisabler disabler(m_frame->document());
     if (m_documentLoader) {
         client()->dispatchWillClose();
         dispatchUnloadEvent();