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

Source/core/html/parser/HTMLTreeBuilder.h

Index: Source/core/html/parser/HTMLTreeBuilder.h
diff --git a/Source/core/html/parser/HTMLTreeBuilder.h b/Source/core/html/parser/HTMLTreeBuilder.h
index d2b541b79ca5fc5e9decc85be9acc69af39c98d6..eac5e6c8f8eb83b0d7c3123c398ca15a09fc6090 100644
--- a/Source/core/html/parser/HTMLTreeBuilder.h
+++ b/Source/core/html/parser/HTMLTreeBuilder.h
@@ -82,8 +82,9 @@
     // Done, close any open tags, etc.
     void finished();
 
-    // Synchronously empty any queues, possibly creating more DOM nodes.
-    void flush() { m_tree.flush(); }
+    // Synchronously flush pending text and queued tasks, possibly creating more DOM nodes.
+    // Flushing pending text depends on |mode|.
+    void flush(FlushMode mode) { m_tree.flush(mode); }
 
     void setShouldSkipLeadingNewline(bool shouldSkip) { m_shouldSkipLeadingNewline = shouldSkip; }