Remove dart backend

test/dart_codegen/expect/core/stopwatch.dart

-part of dart.core;
- class Stopwatch {int get frequency => _frequency;
- num _start;
- num _stop;
- Stopwatch() {
-  _initTicker();
-  }
- void start() {
-  if (isRunning) return; if (_start == null) {
-    _start = _now();
-    }
-   else {
-    _start = _now() - (_stop - _start);
-     _stop = null;
-    }
-  }
- void stop() {
-  if (!isRunning) return; _stop = _now();
-  }
- void reset() {
-  if (_start == null) return; _start = _now();
-   if (_stop != null) {
-    _stop = _start;
-    }
-  }
- int get elapsedTicks {
-  if (_start == null) {
-    return 0;
-    }
-   return ((__x20) => DEVC$RT.cast(__x20, num, int, "ImplicitCast", """line 102, column 12 of dart:core/stopwatch.dart: """, __x20 is int, true))((_stop == null) ? (_now() - _start) : (_stop - _start));
-  }
- Duration get elapsed {
-  return new Duration(microseconds: elapsedMicroseconds);
-  }
- int get elapsedMicroseconds {
-  return (elapsedTicks * 1000000) ~/ frequency;
-  }
- int get elapsedMilliseconds {
-  return (elapsedTicks * 1000) ~/ frequency;
-  }
- bool get isRunning => _start != null && _stop == null;
- static int _frequency;
- external static void _initTicker();
- external static int _now();
-}