Add type inference for break and continue statements.

pkg/front_end/testcases/inference/switch_continue.dart

+// Copyright (c) 2017, 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.
+
+/*@testedFeatures=inference*/
+library test;
+
+// Note: there are no expectations to fulfill here; we just want to make sure
+// that inference completes without crashing.
+
+void test(int x, void f()) {
+  switch (x) {
+    case 0:
+      f();
+      continue L;
+    L:
+    case 1:
+      f();
+      break;
+  }
+}
+
+main() {}