Fix problems with flakes in SVG LayoutTests by reordering arithmetic.

Source/core/svg/SVGLengthContext.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.
  * Copyright (C) Research In Motion Limited 2011. 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 34 matching lines @@
 {
     RefPtrWillBeRawPtr<SVGLength> x = passX;
     RefPtrWillBeRawPtr<SVGLength> y = passY;
     RefPtrWillBeRawPtr<SVGLength> width = passWidth;
     RefPtrWillBeRawPtr<SVGLength> height = passHeight;
 
     ASSERT(type != SVGUnitTypes::SVG_UNIT_TYPE_UNKNOWN);
     if (type != SVGUnitTypes::SVG_UNIT_TYPE_USERSPACEONUSE && !viewport.isEmpty()) {
         const FloatSize& viewportSize = viewport.size();
         return FloatRect(
-            convertValueFromPercentageToUserUnits(x->valueAsPercentage(), x->unitMode(), viewportSize) + viewport.x(),
-            convertValueFromPercentageToUserUnits(y->valueAsPercentage(), y->unitMode(), viewportSize) + viewport.y(),
-            convertValueFromPercentageToUserUnits(width->valueAsPercentage(), width->unitMode(), viewportSize),
-            convertValueFromPercentageToUserUnits(height->valueAsPercentage(), height->unitMode(), viewportSize));
+            convertValueFromPercentageToUserUnits(*x, viewportSize) + viewport.x(),
+            convertValueFromPercentageToUserUnits(*y, viewportSize) + viewport.y(),
+            convertValueFromPercentageToUserUnits(*width, viewportSize),
+            convertValueFromPercentageToUserUnits(*height, viewportSize));
     }
 
     SVGLengthContext lengthContext(context);
     return FloatRect(x->value(lengthContext), y->value(lengthContext), width->value(lengthContext), height->value(lengthContext));
 }
 
 FloatPoint SVGLengthContext::resolvePoint(const SVGElement* context, SVGUnitTypes::SVGUnitType type, PassRefPtrWillBeRawPtr<SVGLength> passX, PassRefPtrWillBeRawPtr<SVGLength> passY)
 {
     RefPtrWillBeRawPtr<SVGLength> x = passX;
     RefPtrWillBeRawPtr<SVGLength> y = passY;
@@ skipping 26 matching lines @@
 {
     switch (fromUnit) {
     case LengthTypeUnknown:
         exceptionState.throwDOMException(NotSupportedError, ExceptionMessages::argumentNullOrIncorrectType(3, "SVGLengthType"));
         return 0;
     case LengthTypeNumber:
         return value;
     case LengthTypePX:
         return value;
     case LengthTypePercentage:
-        return convertValueFromPercentageToUserUnits(value / 100, mode, exceptionState);
+        return convertValueFromPercentageToUserUnits(value, mode, exceptionState) / 100;
     case LengthTypeEMS:
         return convertValueFromEMSToUserUnits(value, exceptionState);
     case LengthTypeEXS:
         return convertValueFromEXSToUserUnits(value, exceptionState);
     case LengthTypeCM:
         return value * cssPixelsPerCentimeter;
     case LengthTypeMM:
         return value * cssPixelsPerMillimeter;
     case LengthTypeIN:
         return value * cssPixelsPerInch;
@@ skipping 78 matching lines @@
     case LengthModeHeight:
         return value * viewportSize.height();
     case LengthModeOther:
         return value * sqrtf(viewportSize.diagonalLengthSquared() / 2);
     };
 
     ASSERT_NOT_REACHED();
     return 0;
 }
 
+float SVGLengthContext::convertValueFromPercentageToUserUnits(const SVGLength& value, const FloatSize& viewportSize)
+{
+    float resultValue;
+    switch (value.unitMode()) {
+    default:
+        ASSERT_NOT_REACHED();

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

I'd prefer to structure this new function like the previous - i.e. tail-calls
and ASSERT_NOT_REACHED() outside the switch.

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

Ok.

I do like this structure though because it generates more efficient code and
won't contain dummy return values put there to silence compilers, but instead
causing confusion in code analyzers.

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

Well saying that it generates better code is a bold statement IMO =) (plenty of
things to fubar in this version too.) And the dummy return value is instead
replaced by a dummy switch-case. (Also, if ASSERT_NOT_REACHED is implemented in
a meaningful way, that edge will be dead in practice.)

+        // Fall through.
+    case LengthModeWidth:
+        resultValue = value.scaleByPercentage(viewportSize.width());
+        break;
+    case LengthModeHeight:
+        resultValue = value.scaleByPercentage(viewportSize.height());
+        break;
+    case LengthModeOther:
+        resultValue = value.scaleByPercentage(sqrtf(viewportSize.diagonalLengthSquared() / 2));
+        break;
+    };
+
+    return resultValue;
+}
+
 static inline RenderStyle* renderStyleForLengthResolving(const SVGElement* context)
 {
     if (!context)
         return 0;
 
     const ContainerNode* currentContext = context;
     do {
         if (currentContext->renderer())
             return currentContext->renderer()->style();
         currentContext = currentContext->parentNode();
@@ skipping 82 matching lines @@
 
     const SVGSVGElement& svg = toSVGSVGElement(*viewportElement);
     viewportSize = svg.currentViewBoxRect().size();
     if (viewportSize.isEmpty())
         viewportSize = svg.currentViewportSize();
 
     return true;
 }
 
 }