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

Source/core/html/forms/RangeInputType.cpp

Index: Source/core/html/forms/RangeInputType.cpp
diff --git a/Source/core/html/forms/RangeInputType.cpp b/Source/core/html/forms/RangeInputType.cpp
index b688e7462adfdf214b4134c490b632d94883bf93..5177ab18bd9700c4ce5cff745f88b68bdd32085b 100644
--- a/Source/core/html/forms/RangeInputType.cpp
+++ b/Source/core/html/forms/RangeInputType.cpp
@@ -124,8 +124,8 @@ StepRange RangeInputType::createStepRange(AnyStepHandling anyStepHandling) const
 {
     DEFINE_STATIC_LOCAL(const StepRange::StepDescription, stepDescription, (rangeDefaultStep, rangeDefaultStepBase, rangeStepScaleFactor));
 
-    const Decimal minimum = parseToNumber(element().fastGetAttribute(minAttr), rangeDefaultMinimum);
-    const Decimal maximum = ensureMaximum(parseToNumber(element().fastGetAttribute(maxAttr), rangeDefaultMaximum), minimum, rangeDefaultMaximum);
+    const Decimal minimum = parseToNumber(element().fastGetAttribute(minAttr), String(), rangeDefaultMinimum);
+    const Decimal maximum = ensureMaximum(parseToNumber(element().fastGetAttribute(maxAttr), String(), rangeDefaultMaximum), minimum, rangeDefaultMaximum);
 
     const AtomicString& precisionValue = element().fastGetAttribute(precisionAttr);
     if (!precisionValue.isNull()) {
@@ -259,8 +259,15 @@ RenderObject* RangeInputType::createRenderer(RenderStyle*) const
     return new RenderSlider(&element());
 }
 
-Decimal RangeInputType::parseToNumber(const String& src, const Decimal& defaultValue) const
+Decimal RangeInputType::parseToNumber(const String& src, const String& alternative, const Decimal& defaultValue) const
 {
+    if (!alternative.isEmpty()) {
+        Decimal result = parseToDecimalForNumberType(src, Decimal::nan());
+        if (!result.isFinite())
+            result = parseToDecimalForNumberType(alternative, defaultValue);
+
+        return result;
+    }
     return parseToDecimalForNumberType(src, defaultValue);
 }
 
@@ -305,7 +312,7 @@ String RangeInputType::fallbackValue() const
 String RangeInputType::sanitizeValue(const String& proposedValue) const
 {
     StepRange stepRange(createStepRange(RejectAny));
-    const Decimal proposedNumericValue = parseToNumber(proposedValue, stepRange.defaultValue());
+    const Decimal proposedNumericValue = parseToNumber(proposedValue, String(), stepRange.defaultValue());
     return serializeForNumberType(stepRange.clampValue(proposedNumericValue));
 }
 
@@ -354,7 +361,7 @@ void RangeInputType::updateTickMarkValues()
         String optionValue = optionElement->value();
         if (!element().isValidValue(optionValue))
             continue;
-        m_tickMarkValues.append(parseToNumber(optionValue, Decimal::nan()));
+        m_tickMarkValues.append(parseToNumber(optionValue, String(), Decimal::nan()));
     }
     m_tickMarkValues.shrinkToFit();
     nonCopyingSort(m_tickMarkValues.begin(), m_tickMarkValues.end(), decimalCompare);