Factor out common StepRange construction code.

Source/core/html/forms/WeekInputType.cpp

Index: Source/core/html/forms/WeekInputType.cpp
diff --git a/Source/core/html/forms/WeekInputType.cpp b/Source/core/html/forms/WeekInputType.cpp
index 62acb746036bb6ed65b96adea72fa2567ba0df7e..da5550acf54013d0fe116ba2a06f35402409d7df 100644
--- a/Source/core/html/forms/WeekInputType.cpp
+++ b/Source/core/html/forms/WeekInputType.cpp
@@ -72,11 +72,7 @@ StepRange WeekInputType::createStepRange(AnyStepHandling anyStepHandling) const
 {
     DEFINE_STATIC_LOCAL(const StepRange::StepDescription, stepDescription, (weekDefaultStep, weekDefaultStepBase, weekStepScaleFactor, StepRange::ParsedStepValueShouldBeInteger));
 
-    const Decimal stepBase = findStepBase(weekDefaultStepBase);
-    const Decimal minimum = parseToNumber(element().fastGetAttribute(minAttr), Decimal::fromDouble(DateComponents::minimumWeek()));
-    const Decimal maximum = parseToNumber(element().fastGetAttribute(maxAttr), Decimal::fromDouble(DateComponents::maximumWeek()));
-    const Decimal step = StepRange::parseStep(anyStepHandling, stepDescription, element().fastGetAttribute(stepAttr));
-    return StepRange(stepBase, minimum, maximum, step, stepDescription);
+    return InputType::createStepRange(anyStepHandling, weekDefaultStepBase, Decimal::fromDouble(DateComponents::minimumWeek()), Decimal::fromDouble(DateComponents::maximumWeek()), stepDescription);
 }
 
 bool WeekInputType::parseToDateComponentsInternal(const String& string, DateComponents* out) const