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..32a937324ca52d7050c5b39aecf124e4a1a406e4 100644
--- a/Source/core/html/forms/MonthInputType.cpp
+++ b/Source/core/html/forms/MonthInputType.cpp
@@ -108,17 +108,17 @@ 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 minimum = parseToNumber(element().fastGetAttribute(minAttr), Decimal::fromDouble(DateComponents::minimumMonth()));
-    const Decimal maximum = parseToNumber(element().fastGetAttribute(maxAttr), Decimal::fromDouble(DateComponents::maximumMonth()));
+    const Decimal stepBase = parseToNumber(element().fastGetAttribute(minAttr), element().fastGetAttribute(minAttr), Decimal::fromDouble(monthDefaultStepBase));
+    const Decimal minimum = parseToNumber(element().fastGetAttribute(minAttr), String(), Decimal::fromDouble(DateComponents::minimumMonth()));
+    const Decimal maximum = parseToNumber(element().fastGetAttribute(maxAttr), String(), Decimal::fromDouble(DateComponents::maximumMonth()));
     const Decimal step = StepRange::parseStep(anyStepHandling, stepDescription, element().fastGetAttribute(stepAttr));
     return StepRange(stepBase, minimum, maximum, step, stepDescription);
 }
 
-Decimal MonthInputType::parseToNumber(const String& src, const Decimal& defaultValue) const
+Decimal MonthInputType::parseToNumber(const String& src, const String& alternative, const Decimal& defaultValue) const
 {
     DateComponents date;
-    if (!parseToDateComponents(src, &date))
+    if (!parseToDateComponents(src, &date) && !parseToDateComponents(alternative, &date))
         return defaultValue;
     double months = date.monthsSinceEpoch();
     ASSERT(std::isfinite(months));