Fix crash in isDocumentDoneLoading()

Document::loader() might be null if re-entrancy is involved.

BUG=357570

Review URL: https://codereview.chromium.org/222433003

git-svn-id: svn://svn.chromium.org/blink/trunk@170693 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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

@@ -912,6 +912,8 @@ FrameLoadType FrameLoader::loadType() const
 // If you're thinking of using it elsewhere, stop right now and reconsider your life.
 static bool isDocumentDoneLoading(Document* document)
 {
+    if (!document->loader())
+        return true;
     if (document->loader()->isLoadingMainResource())
         return false;
     if (!document->loadEventFinished()) {