Switch-implementation.

frog/leg/lib/js_helper.dart

Index: frog/leg/lib/js_helper.dart
diff --git a/frog/leg/lib/js_helper.dart b/frog/leg/lib/js_helper.dart
index 20c3e97e13d72a9d0ea6608684d3fce3434982bb..390a07b39c8ba5f288e16b2d703fdde29cb4302c 100644
--- a/frog/leg/lib/js_helper.dart
+++ b/frog/leg/lib/js_helper.dart
@@ -1385,3 +1385,15 @@ bool jsHasOwnProperty(var jsObject, String property) {
 jsPropertyAccess(var jsObject, String property) {
   return JS('var', @'$0[$1]', jsObject, property);
 }
+
+
+// Called at the end of unaborted switch cases to get the (unique)
+// FallThroughError exception that will be thrown.
+FallThroughError fallThroughErrorInstance = null;
+getFallThroughError() {
+  // TODO(lrn): Redo when we support "const FallThroughError()".
+  if (fallThroughErrorInstance === null) {
+    fallThroughErrorInstance = new FallThroughError();
+  }
+  return fallThroughErrorInstance;
+}