Fix problems with flakes in SVG LayoutTests by reordering arithmetic.

Source/core/svg/SVGLength.cpp

 /*
  * Copyright (C) 2004, 2005, 2006 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007 Rob Buis <buis@kde.org>
  * Copyright (C) 2007 Apple Inc. 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 167 matching lines @@
 }
 
 void SVGLength::setUnitType(SVGLengthType type)
 {
     ASSERT(type != LengthTypeUnknown && type <= LengthTypePC);
     m_unitType = type;
 }
 
 float SVGLength::valueAsPercentage() const
 {
     // 100% = 100.0 instead of 1.0 for historical reasons, this could eventually be changed

[Stephen Chennney, 2015/01/22 21:57:25]

This comment seems wrong now.

[Daniel Bratell, 2015/01/23 08:49:40]

It is still correct since it refers to the internal representation of
LengthTypePercentage. I will rephrase them though, so that it's more clear.

-    if (m_unitType == LengthTypePercentage)
+    if (m_unitType == LengthTypePercentage) {
+        // Note: This division is a source of floating point inaccuracy.
         return m_valueInSpecifiedUnits / 100;
+    }
 
     return m_valueInSpecifiedUnits;
 }
 
+float SVGLength::valueAsPercentage100() const
+{
+    // 100% = 100.0 instead of 1.0 for historical reasons, this could eventually be changed
+    if (m_unitType == LengthTypePercentage)
+        return m_valueInSpecifiedUnits;
+
+    return m_valueInSpecifiedUnits * 100;
+}
+
+float SVGLength::scaleByPercentage(float input) const
+{
+    float result = input * m_valueInSpecifiedUnits;
+    if (m_unitType == LengthTypePercentage) {
+        // Delaying division by 100 as long as possible since it introduces floating point errors.
+        result = result / 100;
+    }
+    return result;
+}
+
 template<typename CharType>
 static bool parseValueInternal(const String& string, float& convertedNumber, SVGLengthType& type)
 {
     const CharType* ptr = string.getCharacters<CharType>();
     const CharType* end = ptr + string.length();
 
     if (!parseNumber(ptr, end, convertedNumber, AllowLeadingWhitespace))
         return false;
 
     type = stringToLengthType(ptr, end);
@@ skipping 191 matching lines @@
         || fromType == LengthTypeUnknown
         || toType == LengthTypeUnknown
         || (!from->isZero() && fromType != LengthTypePercentage && toType == LengthTypePercentage)
         || (!isZero() && fromType == LengthTypePercentage && toType != LengthTypePercentage)
         || (!from->isZero() && !isZero() && (fromType == LengthTypeEMS || fromType == LengthTypeEXS) && fromType != toType))
         return clone();
 
     RefPtrWillBeRawPtr<SVGLength> length = create();
 
     if (fromType == LengthTypePercentage || toType == LengthTypePercentage) {
-        float fromPercent = from->valueAsPercentage() * 100;
-        float toPercent = valueAsPercentage() * 100;
+        float fromPercent = from->valueAsPercentage100();
+        float toPercent = valueAsPercentage100();
         length->newValueSpecifiedUnits(LengthTypePercentage, blink::blend(fromPercent, toPercent, progress));
         return length;
     }
 
     if (fromType == toType || from->isZero() || isZero() || fromType == LengthTypeEMS || fromType == LengthTypeEXS) {
         float fromValue = from->valueInSpecifiedUnits();
         float toValue = valueInSpecifiedUnits();
         if (isZero())
             length->newValueSpecifiedUnits(fromType, blink::blend(fromValue, toValue, progress));
         else
@@ skipping 43 matching lines @@
 
 float SVGLength::calculateDistance(PassRefPtrWillBeRawPtr<SVGPropertyBase> toValue, SVGElement* contextElement)
 {
     SVGLengthContext lengthContext(contextElement);
     RefPtrWillBeRawPtr<SVGLength> toLength = toSVGLength(toValue);
 
     return fabsf(toLength->value(lengthContext, IGNORE_EXCEPTION) - value(lengthContext, IGNORE_EXCEPTION));
 }
 
 }