DocumentParser should flush itself on finish

Source/core/html/parser/HTMLDocumentParser.cpp

Index: Source/core/html/parser/HTMLDocumentParser.cpp
diff --git a/Source/core/html/parser/HTMLDocumentParser.cpp b/Source/core/html/parser/HTMLDocumentParser.cpp
index 5c78b8da1b9df2032bc0b121f5b8c57315bec37e..e430d15ea5b93ae29149cc2efc4918cb578472e7 100644
--- a/Source/core/html/parser/HTMLDocumentParser.cpp
+++ b/Source/core/html/parser/HTMLDocumentParser.cpp
@@ -872,6 +872,12 @@ void HTMLDocumentParser::finish()
     // makes sense to call any methods on DocumentParser once it's been stopped.
     // However, FrameLoader::stop calls DocumentParser::finish unconditionally.
 
+    // flush may ending up executing arbitrary script, and possibly detach the parser.
+    RefPtr<HTMLDocumentParser> protect(this);
+    flush();
+    if (isDetached())
+        return;
+
     // Empty documents never got an append() call, and thus have never started
     // a background parser. In those cases, we ignore shouldUseThreading()
     // and fall through to the non-threading case.