Fix problems with flakes in SVG LayoutTests.

Source/core/rendering/svg/SVGRenderTreeAsText.cpp

 /*
  * Copyright (C) 2004, 2005, 2007, 2009 Apple Inc. All rights reserved.
  *           (C) 2005 Rob Buis <buis@kde.org>
  *           (C) 2006 Alexander Kellett <lypanov@kde.org>
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
@@ skipping 309 matching lines @@
             ts << "}]";
         }
         writeIfNotDefault(ts, "clip rule", svgStyle.clipRule(), RULE_NONZERO);
     }
 
     writeIfNotEmpty(ts, "start marker", svgStyle.markerStartResource());
     writeIfNotEmpty(ts, "middle marker", svgStyle.markerMidResource());
     writeIfNotEmpty(ts, "end marker", svgStyle.markerEndResource());
 }
 
+static float snapToCloseInteger(float value)
+{
+    // Due to floating point arithmetic uncertainties we may sometimes end up at
+    // something like 4.99999952 when pure arithmetic would have given 5.
+    // To give predictable results in debug ouput, snap numbers very close to
+    // integers to integers. This matters because sometimes numbers are truncated
+    // rather than rounded before being viewed as integers.
+    const double epsilon = 0.00001;
+    if (fabs(value - round(value)) < epsilon)
+        return static_cast<float>(round(value));
+    return value;
+}
+
+static FloatPoint snapToCloseInteger(FloatPoint point)
+{
+    return FloatPoint(snapToCloseInteger(point.x()), snapToCloseInteger(point.y()));
+}
+
+static FloatRect snapToCloseInteger(FloatRect rect)
+{
+    FloatPoint bottomRight = snapToCloseInteger(rect.maxXMaxYCorner());
+    FloatPoint topLeft = snapToCloseInteger(rect.minXMinYCorner());
+    return FloatRect(topLeft, bottomRight - topLeft);
+}
+
 static TextStream& writePositionAndStyle(TextStream& ts, const RenderObject& object)
 {
-    ts << " " << enclosingIntRect(const_cast<RenderObject&>(object).absoluteClippedOverflowRect());
+    FloatRect rect = snapToCloseInteger(object.absoluteClippedOverflowRect());

[Daniel Bratell, 2015/01/22 09:21:40]

This is too late. It's in the conversion from float to LayoutRect the large
error is introduced.

+    ts << " " << enclosingIntRect(rect);
     writeStyle(ts, object);
     return ts;
 }
 
 static TextStream& operator<<(TextStream& ts, const RenderSVGShape& shape)
 {
     writePositionAndStyle(ts, shape);
 
     SVGElement* svgElement = shape.element();
     ASSERT(svgElement);
@@ skipping 331 matching lines @@
             ts << " ";
             writeNameAndQuotedValue(ts, "filter", svgStyle.filterResource());
             ts << " ";
             writeStandardPrefix(ts, *filter, 0);
             ts << " " << filter->resourceBoundingBox(&renderer) << "\n";
         }
     }
 }
 
 } // namespace blink