Compile implicit closures as dispatchers instead of duplicating the original method's code.

tests/standalone/full_coverage_test.dart

Index: tests/standalone/full_coverage_test.dart
===================================================================
--- tests/standalone/full_coverage_test.dart	(revision 44654)
+++ tests/standalone/full_coverage_test.dart	(working copy)
@@ -49,7 +49,7 @@
   }
 }
 ''',
-    'expectedHits': [-1, 0, 0, -1, -1, -1, -1, -1, 1, 1, -1, -1, -1, -1, -1, -1,
+    'expectedHits': [-1, 0, 0, -1, -1, -1, -1, -1, 1, 1, -1, -1, -1, -1, 1, -1,
                      0, -1, 1, -1, -1]
   },{
     'name': 'closures',
@@ -64,7 +64,7 @@
   });
 }
 ''',
-    'expectedHits': [-1, -1, 1, -1, -1, 1, 1, -1, -1]
+    'expectedHits': [1, -1, 1, -1, -1, 1, 1, -1, -1]
   }
 ];