Derive the step base for an input element as (now) specified.

Source/core/html/forms/MonthInputType.cpp

Index: Source/core/html/forms/MonthInputType.cpp
diff --git a/Source/core/html/forms/MonthInputType.cpp b/Source/core/html/forms/MonthInputType.cpp
index 3003558693df0ab5e7ef9c346b4431894d1f6fea..5aed90b5e70aa0cd3d20c786cc8d09ac314c63d5 100644
--- a/Source/core/html/forms/MonthInputType.cpp
+++ b/Source/core/html/forms/MonthInputType.cpp
@@ -108,7 +108,7 @@ StepRange MonthInputType::createStepRange(AnyStepHandling anyStepHandling) const
 {
     DEFINE_STATIC_LOCAL(const StepRange::StepDescription, stepDescription, (monthDefaultStep, monthDefaultStepBase, monthStepScaleFactor, StepRange::ParsedStepValueShouldBeInteger));
 
-    const Decimal stepBase = parseToNumber(element().fastGetAttribute(minAttr), Decimal::fromDouble(monthDefaultStepBase));
+    const Decimal stepBase = findStepBase(Decimal::fromDouble(monthDefaultStepBase));
     const Decimal minimum = parseToNumber(element().fastGetAttribute(minAttr), Decimal::fromDouble(DateComponents::minimumMonth()));
     const Decimal maximum = parseToNumber(element().fastGetAttribute(maxAttr), Decimal::fromDouble(DateComponents::maximumMonth()));
     const Decimal step = StepRange::parseStep(anyStepHandling, stepDescription, element().fastGetAttribute(stepAttr));