Simplify the desugaring of catch clauses.

tests/language/try_catch_test.dart

 // Copyright (c) 2011, 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.
 // VMOptions=--optimization-counter-threshold=10
 
 import "package:expect/expect.dart";
 
 class MyException { }
 
 class MyException1 extends MyException { }
@@ skipping 129 matching lines @@
 
   static void test10() {
     try {
       throw "up";
     } on String catch (e) {
       var e = 1;  // ok, shadows exception variable.
       Expect.equals(1, e);
     }
   }
 
+  static void test11() {
+    var e0 = 11;
+    try {
+      throw "up";
+    } on int catch (e0) {
+      Expect.fail("unreachable");
+    } on String catch (e1) {
+      // e0 from the other catch clause is not in scope.
+      Expect.equals(11, e0);
+    }
+  }
+
+  static void test12() {
+    const x = const [];
+    try {
+      throw "up";
+    } catch (e) {
+      Expect.equals("up", e);
+    } on String catch (e) {
+      // Compile-time constants in unreachable catch blocks are still
+      // compiled.
+      const y = x[0];  /// 01: compile-time error
+      Expect.fail("unreachable");
+    }
+  }
+      
+
   static void testMain() {
     test1();
     test2();
     test3();
     test4();
     test5();
     test6();
     test7();
     test8();
     test9();
     test10();
+    test11();
+    test12();
   }
 }
 
 main() {
   for (var i = 0; i < 20; i++) {
     TryCatchTest.testMain();
   }
 }