Add types on internal DateTime accessors

sdk/lib/_internal/js_runtime/lib/js_helper.dart

Index: sdk/lib/_internal/js_runtime/lib/js_helper.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/js_helper.dart b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
index 5e4d69aca847eec66f76ea172b3f41abbeceb0ad..6cfcda8d7cb9a8c1d3d255b436f073557cae38ee 100644
--- a/sdk/lib/_internal/js_runtime/lib/js_helper.dart
+++ b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
@@ -1039,7 +1039,7 @@ class Primitives {
     return JS('String', "#.charCodeAt(0) == 0 ? # : #", str, str, str);
   }
 
-  static String getTimeZoneName(receiver) {
+  static String getTimeZoneName(DateTime receiver) {
     // Firefox and Chrome emit the timezone in parenthesis.
     // Example: "Wed May 16 2012 21:13:00 GMT+0200 (CEST)".
     // We extract this name using a regexp.
@@ -1073,7 +1073,7 @@ class Primitives {
     return "";
   }
 
-  static int getTimeZoneOffsetInMinutes(receiver) {
+  static int getTimeZoneOffsetInMinutes(DateTime receiver) {
     // Note that JS and Dart disagree on the sign of the offset.
     return -JS('int', r'#.getTimezoneOffset()', lazyAsJsDate(receiver));
   }
@@ -1118,7 +1118,7 @@ class Primitives {
   }
 
   // Lazily keep a JS Date stored in the JS object.
-  static lazyAsJsDate(receiver) {
+  static lazyAsJsDate(DateTime receiver) {
     if (JS('bool', r'#.date === (void 0)', receiver)) {
       JS('void', r'#.date = new Date(#)', receiver,
          receiver.millisecondsSinceEpoch);
@@ -1130,49 +1130,49 @@ class Primitives {
   // that the result is really an integer, because the JavaScript implementation
   // may return -0.0 instead of 0.
 
-  static getYear(receiver) {
+  static getYear(DateTime receiver) {
     return (receiver.isUtc)
       ? JS('int', r'(#.getUTCFullYear() + 0)', lazyAsJsDate(receiver))
       : JS('int', r'(#.getFullYear() + 0)', lazyAsJsDate(receiver));
   }
 
-  static getMonth(receiver) {
+  static getMonth(DateTime receiver) {
     return (receiver.isUtc)
       ? JS('JSUInt31', r'#.getUTCMonth() + 1', lazyAsJsDate(receiver))
       : JS('JSUInt31', r'#.getMonth() + 1', lazyAsJsDate(receiver));
   }
 
-  static getDay(receiver) {
+  static getDay(DateTime receiver) {
     return (receiver.isUtc)
       ? JS('JSUInt31', r'(#.getUTCDate() + 0)', lazyAsJsDate(receiver))
       : JS('JSUInt31', r'(#.getDate() + 0)', lazyAsJsDate(receiver));
   }
 
-  static getHours(receiver) {
+  static getHours(DateTime receiver) {
     return (receiver.isUtc)
       ? JS('JSUInt31', r'(#.getUTCHours() + 0)', lazyAsJsDate(receiver))
       : JS('JSUInt31', r'(#.getHours() + 0)', lazyAsJsDate(receiver));
   }
 
-  static getMinutes(receiver) {
+  static getMinutes(DateTime receiver) {
     return (receiver.isUtc)
       ? JS('JSUInt31', r'(#.getUTCMinutes() + 0)', lazyAsJsDate(receiver))
       : JS('JSUInt31', r'(#.getMinutes() + 0)', lazyAsJsDate(receiver));
   }
 
-  static getSeconds(receiver) {
+  static getSeconds(DateTime receiver) {
     return (receiver.isUtc)
       ? JS('JSUInt31', r'(#.getUTCSeconds() + 0)', lazyAsJsDate(receiver))
       : JS('JSUInt31', r'(#.getSeconds() + 0)', lazyAsJsDate(receiver));
   }
 
-  static getMilliseconds(receiver) {
+  static getMilliseconds(DateTime receiver) {
     return (receiver.isUtc)
       ? JS('JSUInt31', r'(#.getUTCMilliseconds() + 0)', lazyAsJsDate(receiver))
       : JS('JSUInt31', r'(#.getMilliseconds() + 0)', lazyAsJsDate(receiver));
   }
 
-  static getWeekday(receiver) {
+  static getWeekday(DateTime receiver) {
     int weekday = (receiver.isUtc)
       ? JS('int', r'#.getUTCDay() + 0', lazyAsJsDate(receiver))
       : JS('int', r'#.getDay() + 0', lazyAsJsDate(receiver));