Rename StopWatch to Stopwatch. Add new Stopwatch.start() and Stopwatch.reset().

tests/corelib/src/StopWatchTest.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-// Dart test program for testing stopwatch support.
-
-class StopWatchTest {
-  static bool checkTicking(StopWatch sw) {
-    sw.start();
-    for (int i = 0; i < 10000; i++) {
-      Math.parseInt(i.toString());
-      if (sw.elapsed() > 0) {
-        break;
-      }
-    }
-    return sw.elapsed() > 0;
-  }
-
-  static bool checkStopping(StopWatch sw) {
-    sw.stop();
-    int v1 = sw.elapsed();
-    Expect.isTrue(v1 > 0);  // Expect a non-zero elapsed time.
-    StopWatch sw2 = new StopWatch();  // Used for verification.
-    sw2.start();
-    for (int i = 0; i < 10000; i++) {
-      Math.parseInt(i.toString());
-      int v2 = sw.elapsed();
-      if (v1 != v2) {
-        return false;
-      }
-      v1 = v2;
-    }
-    // The test only makes sense if measureable time elapsed and elapsed time
-    // on the stopped StopWatch did not increase.
-    Expect.isTrue(sw2.elapsed() > 0);
-    return true;
-  }
-
-  static checkRestart() {
-    StopWatch sw = new StopWatch();
-    sw.start();
-    for (int i = 0; i < 1000; i++) {
-      Math.parseInt(i.toString());
-    }
-    sw.stop();
-    int initial = sw.elapsed();
-    sw.start();
-    for (int i = 0; i < 10; i++) {
-      Math.parseInt(i.toString());
-    }
-    sw.stop();
-    Expect.isTrue(sw.elapsed() >= initial);
-  }
-
-  static testMain() {
-    StopWatch sw = new StopWatch();
-    Expect.isTrue(checkTicking(sw));
-    Expect.isTrue(checkStopping(sw));
-    checkRestart();
-  }
-}
-
-main() {
-  StopWatchTest.testMain();
-}