Fix problems with flakes in SVG LayoutTests by reordering arithmetic.

Source/core/svg/SVGLength.cpp

Index: Source/core/svg/SVGLength.cpp
diff --git a/Source/core/svg/SVGLength.cpp b/Source/core/svg/SVGLength.cpp
index 3c928704dc21593d6dd2cd672f1f622760e1dea7..10db3a15c50f7b27e3198469354636cfb07e5e0e 100644
--- a/Source/core/svg/SVGLength.cpp
+++ b/Source/core/svg/SVGLength.cpp
@@ -186,12 +186,33 @@ void SVGLength::setUnitType(SVGLengthType type)
 float SVGLength::valueAsPercentage() const
 {
     // 100% = 100.0 instead of 1.0 for historical reasons, this could eventually be changed
-    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

[fs, 2015/01/22 12:37:36]

Given the specific name - but generic function - maybe this should be scaleBy()
or only have the percentage-branch (and assert that type==percentage).

[Daniel Bratell, 2015/01/22 13:13:44]

Judging from how the code was used, it seems code handled "0.1" and "10%" the
same. There is for instance the code below that handles that only one of "from"
and "to" has a percentage sign and the other does not. It would be different
(more cases) if the difference was exposed.

For this code in particular, I just can't see if resolveRectangle is only called
with all of width, height, x and y are percentages.

[fs, 2015/01/22 14:06:35]

Yes, that's true... I suppose I'm still used to percentage being resolved in a
different way.

+{
+    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)
 {
@@ -403,8 +424,8 @@ PassRefPtrWillBeRawPtr<SVGLength> SVGLength::blend(PassRefPtrWillBeRawPtr<SVGLen
     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;
     }