Only use fontMetrics if available in line-height computation

third_party/WebKit/Source/core/style/ComputedStyle.cpp

 /*
  * Copyright (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Adobe Systems Incorporated. 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.
  *
@@ skipping 1289 matching lines @@
 
     return lh;
 }
 
 void ComputedStyle::setLineHeight(const Length& specifiedLineHeight) { SET_VAR(inherited, line_height, specifiedLineHeight); }
 
 int ComputedStyle::computedLineHeight() const
 {
     const Length& lh = lineHeight();
 
-    // Negative value means the line height is not set. Use the font's built-in spacing.
-    if (lh.isNegative())
+    // Negative value means the line height is not set. Use the font's built-in
+    // spacing, if avalible.
+    if (lh.isNegative() && font().primaryFont())
         return fontMetrics().lineSpacing();
 
     if (lh.hasPercent())
         return minimumValueForLength(lh, fontSize());
 
     return std::min(lh.value(), LayoutUnit::max().toFloat());
 }
 
 void ComputedStyle::setWordSpacing(float wordSpacing)
 {
@@ skipping 476 matching lines @@
 }
 
 void ComputedStyle::copyChildDependentFlagsFrom(const ComputedStyle& other)
 {
     setEmptyState(other.emptyState());
     if (other.hasExplicitlyInheritedProperties())
         setHasExplicitlyInheritedProperties();
 }
 
 } // namespace blink