Revert of Revert of HTMLConstructionSite: avoid n^2 running time for large scripts.

Source/core/html/parser/HTMLConstructionSite.h

 /*
  * Copyright (C) 2010 Google, Inc. All Rights Reserved.
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 74 matching lines @@
 namespace blink {
 
 // Note: These are intentionally ordered so that when we concatonate
 // strings and whitespaces the resulting whitespace is ws = min(ws1, ws2).
 enum WhitespaceMode {
     WhitespaceUnknown,
     NotAllWhitespace,
     AllWhitespace,
 };
 
+enum FlushMode {
+    // Flush pending text. Flush queued tasks.
+    FlushAlways,
+
+    // Flush pending text if node has length limit. Flush queued tasks.
+    FlushIfAtTextLimit,
+};
+
 class AtomicHTMLToken;
 class Document;
 class Element;
 class HTMLFormElement;
 
 class HTMLConstructionSite FINAL {
     WTF_MAKE_NONCOPYABLE(HTMLConstructionSite);
     DISALLOW_ALLOCATION();
 public:
     HTMLConstructionSite(Document*, ParserContentPolicy);
     HTMLConstructionSite(DocumentFragment*, ParserContentPolicy);
     ~HTMLConstructionSite();
     void trace(Visitor*);
 
     void detach();
 
     // executeQueuedTasks empties the queue but does not flush pending text.
     // NOTE: Possible reentrancy via JavaScript execution.
     void executeQueuedTasks();
 
     // flushPendingText turns pending text into queued Text insertions, but does not execute them.
-    void flushPendingText();
+    void flushPendingText(FlushMode);
 
     // Called before every token in HTMLTreeBuilder::processToken, thus inlined:
-    void flush()
+    void flush(FlushMode mode)
     {
         if (!hasPendingTasks())
             return;
-        flushPendingText();
+        flushPendingText(mode);
         executeQueuedTasks(); // NOTE: Possible reentrancy via JavaScript execution.
-        ASSERT(!hasPendingTasks());
+        ASSERT(mode == FlushIfAtTextLimit || !hasPendingTasks());
     }
 
     bool hasPendingTasks()
     {
         return !m_pendingText.isEmpty() || !m_taskQueue.isEmpty();
     }
 
     void setDefaultCompatibilityMode();
     void processEndOfFile();
     void finishedParsing();
@@ skipping 171 matching lines @@
     // "whenever a node would be inserted into the current node, it must instead
     // be foster parented."  This flag tracks whether we're in that state.
     bool m_redirectAttachToFosterParent;
 
     bool m_inQuirksMode;
 };
 
 } // namespace blink
 
 #endif