Don't duplicate switch case code if we fall through to the default case.

tests/compiler/dart2js_extra/switch_test.dart

 // Copyright (c) 2012, 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.
 
 import "package:expect/expect.dart";
 
 switcher(val) {
   var x = 0;
   switch (val) {
     case 1:
@@ skipping 40 matching lines @@
           break;
         } else {
           // Enable when continue to switch-case is implemented.
           continue hest;
         }
       }
   }
   return x;
 }
 
+var x = 0;
+
+@NoInline()
+switcher3(val) {
+  switch(val) {
+    case 1:
+    default:
+      incrementX();
+  }
+}
+
+incrementX() {
+  x++;
+}
+
 badswitches(val) {
   // Test some badly formed switch bodies.
   // 01 - a label/statement without a following case/default.
   // 02 - a label without a following case/default or statement.
   switch (val) {
     foo: break; //    //# 01: compile-time error
     case 2: //        //# 02: compile-time error
     foo: //           //# 02: continued
   }
 }
 
 main() {
   Expect.equals(100, switcher(1));
   Expect.equals(200, switcher(2));
   Expect.equals(300, switcher(3));
   Expect.equals(400, switcher(4));
 
   Expect.equals(100, switcher2(1));
   Expect.equals(100, switcher2(2));
   Expect.equals(200, switcher2(3));
   Expect.equals(200, switcher2(4));
   Expect.equals(200, switcher2(5));
 
+  switcher3(1);
+  Expect.equals(1, x);
+
   badswitches(42);
 }