Bug 1278185 - Implement valueAsNumber and valueAsDate for <input type=month>. r=smaug

dom/html/HTMLInputElement.h

@@ -1036,11 +1036,7 @@ protected:
   /**
    * Returns if valueAsNumber attribute applies for the current type.
    */
-  bool DoesValueAsNumberApply() const
-  {
-    // TODO: this is temporary until bug 888324 is fixed.
-    return DoesMinMaxApply() && mType != NS_FORM_INPUT_MONTH;
-  }
+  bool DoesValueAsNumberApply() const { return DoesMinMaxApply(); }
 
   /**
    * Returns if autocomplete attribute applies for the current type.
@@ -1205,6 +1201,12 @@ protected:
    */
   uint32_t NumberOfDaysInMonth(uint32_t aMonth, uint32_t aYear) const;
 
+  /**
+   * This methods returns the number of months between January 1970 and the
+   * given year and month.
+   */
+  int32_t MonthsSinceJan1970(uint32_t aYear, uint32_t aMonth) const;
+
   /**
    * Returns whether aValue is a valid time as described by HTML specifications:
    * http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#valid-time-string
@@ -1438,6 +1440,11 @@ protected:
   // Float value returned by GetStep() when the step attribute is set to 'any'.
   static const Decimal kStepAny;
 
+  // Maximum year limited by ECMAScript date object range, year <= 275760.
+  static const double kMaximumYear;
+  // Minimum year limited by HTML standard, year >= 1.
+  static const double kMinimumYear;
+
   /**
    * The type of this input (<input type=...>) as an integer.
    * @see nsIFormControl.h (specifically NS_FORM_INPUT_*)