Implement filter primitive subregion for reference CSS filters. This required refactoring determin…

Source/core/platform/graphics/filters/FEOffset.cpp

Index: Source/core/platform/graphics/filters/FEOffset.cpp
diff --git a/Source/core/platform/graphics/filters/FEOffset.cpp b/Source/core/platform/graphics/filters/FEOffset.cpp
index a64c858c608e0209e99e88925bd1206cccf748ba..5080e1c986525f2449d01158b6cc4df392e70652 100644
--- a/Source/core/platform/graphics/filters/FEOffset.cpp
+++ b/Source/core/platform/graphics/filters/FEOffset.cpp
@@ -80,6 +80,16 @@ void FEOffset::determineAbsolutePaintRect()
     setAbsolutePaintRect(enclosingIntRect(paintRect));
 }
 
+FloatRect FEOffset::mapRect(const FloatRect& rect, bool forward)
+{
+    FloatRect result = rect;
+    if (forward)
+        result.move(filter()->applyHorizontalScale(m_dx), filter()->applyHorizontalScale(m_dy));
+    else
+        result.move(-filter()->applyHorizontalScale(m_dx), -filter()->applyHorizontalScale(m_dy));
+    return result;
+}
+
 void FEOffset::applySoftware()
 {
     FilterEffect* in = inputEffect(0);