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

frog/leg/compiler.dart

Index: frog/leg/compiler.dart
diff --git a/frog/leg/compiler.dart b/frog/leg/compiler.dart
index a38105c8475b86bdee235da4cb266ec83d7d66e5..b781c9e8a03eb8faee74bae0d4b8dcf37e3bc03d 100644
--- a/frog/leg/compiler.dart
+++ b/frog/leg/compiler.dart
@@ -118,9 +118,9 @@ class Compiler implements Canceler, Logger {
 
 class CompilerTask {
   final Compiler compiler;
-  final StopWatch watch;
+  final Stopwatch watch;
 
-  CompilerTask(this.compiler) : watch = new StopWatch();
+  CompilerTask(this.compiler) : watch = new Stopwatch();
 
   String get name() => 'Unknown task';
   int get timing() => watch.elapsedInMs();