createPlainText(): avoid a 32k buffer allocation for empty ranges.

Source/core/editing/iterators/TextIterator.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2005 Alexey Proskuryakov.
  *
  * 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 1075 matching lines @@
 
 // --------
 
 template <typename Strategy>
 static String createPlainText(const EphemeralRangeTemplate<Strategy>& range, TextIteratorBehaviorFlags behavior)
 {
     if (range.isNull())
         return emptyString();
 
     TextIteratorAlgorithm<Strategy> it(range.startPosition(), range.endPosition(), behavior);
+
+    if (it.atEnd())
+        return emptyString();
+
     // The initial buffer size can be critical for performance: https://bugs.webkit.org/show_bug.cgi?id=81192
     static const unsigned initialCapacity = 1 << 15;
 
-    unsigned bufferLength = 0;
     StringBuilder builder;
     builder.reserveCapacity(initialCapacity);
 
-    for (; !it.atEnd(); it.advance()) {
+    for (; !it.atEnd(); it.advance())
         it.text().appendTextToStringBuilder(builder);
-        bufferLength += it.length();
-    }
 
-    if (!bufferLength)
+    if (builder.isEmpty())
         return emptyString();
 
     return builder.toString();
 }
 
 String plainText(const EphemeralRange& range, TextIteratorBehaviorFlags behavior)
 {
     return createPlainText<EditingStrategy>(range, behavior);
 }
 
 String plainText(const EphemeralRangeInComposedTree& range, TextIteratorBehaviorFlags behavior)
 {
     return createPlainText<EditingInComposedTreeStrategy>(range, behavior);
 }
 
 template class CORE_TEMPLATE_EXPORT TextIteratorAlgorithm<EditingStrategy>;
 template class CORE_TEMPLATE_EXPORT TextIteratorAlgorithm<EditingInComposedTreeStrategy>;
 
 } // namespace blink