Add microsecond support to DateTime.

sdk/lib/_internal/js_runtime/lib/core_patch.dart

Index: sdk/lib/_internal/js_runtime/lib/core_patch.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/core_patch.dart b/sdk/lib/_internal/js_runtime/lib/core_patch.dart
index 9dd31a4920723f9dbe71d8fb97ee1c43c189daee..dfed0dfa4116521e1ef191569ee08505fb762a42 100644
--- a/sdk/lib/_internal/js_runtime/lib/core_patch.dart
+++ b/sdk/lib/_internal/js_runtime/lib/core_patch.dart
@@ -186,6 +186,18 @@ class Error {
 @patch
 class DateTime {
   @patch
+  DateTime.fromMillisecondsSinceEpoch(int millisecondsSinceEpoch,
+                                      {bool isUtc: false})
+      : this._withValue(millisecondsSinceEpoch, isUtc: isUtc);
+
+  @patch
+  DateTime.fromMicrosecondsSinceEpoch(int microsecondsSinceEpoch,
+                                      {bool isUtc: false})
+      : this._withValue(
+          _microsecondInRoundedMilliseconds(microsecondsSinceEpoch),
+          isUtc: isUtc);
+
+  @patch
   DateTime._internal(int year,
                      int month,
                      int day,
@@ -193,26 +205,38 @@ class DateTime {
                      int minute,
                      int second,
                      int millisecond,
+                     int microsecond,
                      bool isUtc)
         // checkBool is manually inlined here because dart2js doesn't inline it
         // and [isUtc] is usually a constant.
       : this.isUtc = isUtc is bool
             ? isUtc
             : throw new ArgumentError.value(isUtc, 'isUtc'),
-        millisecondsSinceEpoch = checkInt(Primitives.valueFromDecomposedDate(
-            year, month, day, hour, minute, second, millisecond, isUtc));
+        _value = checkInt(Primitives.valueFromDecomposedDate(
+            year, month, day, hour, minute, second,
+            millisecond + _microsecondInRoundedMilliseconds(microsecond),
+            isUtc));
 
   @patch
   DateTime._now()
       : isUtc = false,
-        millisecondsSinceEpoch = Primitives.dateNow();
+        _value = Primitives.dateNow();
+
+  /// Rounds the given [microsecond] to the nearest milliseconds value.
+  ///
+  /// For example, invoked with argument `2600` returns `3`.
+  static int _microsecondInRoundedMilliseconds(int microsecond) {
+    return (microsecond / 1000).round();
+  }
 
   @patch
-  static int _brokenDownDateToMillisecondsSinceEpoch(
+  static int _brokenDownDateToValue(
       int year, int month, int day, int hour, int minute, int second,
-      int millisecond, bool isUtc) {
+      int millisecond, int microsecond, bool isUtc) {
     return Primitives.valueFromDecomposedDate(
-        year, month, day, hour, minute, second, millisecond, isUtc);
+        year, month, day, hour, minute, second,
+        millisecond + _microsecondInRoundedMilliseconds(microsecond),
+        isUtc);
   }
 
   @patch
@@ -228,6 +252,29 @@ class DateTime {
   }
 
   @patch
+  DateTime add(Duration duration) {
+    return new DateTime._withValue(
+        _value + duration.inMilliseconds, isUtc: isUtc);
+  }
+
+  @patch
+  DateTime subtract(Duration duration) {
+    return new DateTime._withValue(
+        _value - duration.inMilliseconds, isUtc: isUtc);
+  }
+
+  @patch
+  Duration difference(DateTime other) {
+    return new Duration(milliseconds: _value - other._value);
+  }
+
+  @patch
+  int get millisecondsSinceEpoch => _value;
+
+  @patch
+  int get microsecondsSinceEpoch => _value * 1000;
+
+  @patch
   int get year => Primitives.getYear(this);
 
   @patch
@@ -249,6 +296,9 @@ class DateTime {
   int get millisecond => Primitives.getMilliseconds(this);
 
   @patch
+  int get microsecond => 0;
+
+  @patch
   int get weekday => Primitives.getWeekday(this);
 }