Do not crash when measuring empty SVG text nodes

third_party/WebKit/Source/core/layout/svg/SVGTextMetricsBuilder.cpp

 /*
  * Copyright (C) Research In Motion Limited 2010-2012. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 181 matching lines @@
 
     SVGTextLayoutAttributes* attributes = text->layoutAttributes();
     Vector<SVGTextMetrics>* textMetricsValues = &attributes->textMetricsValues();
     if (processLayoutObject) {
         if (data->allCharactersMap)
             attributes->clear();
         else
             textMetricsValues->clear();
     }
 
+    if (!text->textLength())
+        return;
+
     // TODO(pdr): This loop is too tightly coupled to SVGTextMetricsCalculator.
     // We should refactor SVGTextMetricsCalculator to be a simple bidi run
     // iterator and move all subrun logic to a single function.
     SVGTextMetricsCalculator calculator(text);
     bool preserveWhiteSpace = text->style()->whiteSpace() == PRE;
     unsigned surrogatePairCharacters = 0;
     unsigned skippedCharacters = 0;
     do {
         SVGTextMetrics metrics = calculator.currentCharacterMetrics();
         if (!metrics.length())
@@ skipping 62 matching lines @@
 }
 
 void SVGTextMetricsBuilder::buildMetricsAndLayoutAttributes(LayoutSVGText* textRoot, LayoutSVGInlineText* stopAtLeaf, SVGCharacterDataMap& allCharactersMap)
 {
     ASSERT(textRoot);
     MeasureTextData data(&allCharactersMap);
     walkTree(textRoot, stopAtLeaf, &data);
 }
 
 } // namespace blink