Update almost all tests (except co19) to use the new try-catch syntax.

tests/corelib/set_iterator_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.
 
 class FixedHashCode implements Hashable {
   final int _hashCode;
   const FixedHashCode(this._hashCode);
   int hashCode() { return _hashCode; }
 }
 
 class SetIteratorTest {
   static testMain() {
     testSmallSet();
     testLargeSet();
     testEmptySet();
     testSetWithDeletedEntries();
     testBug5116829();
     testDifferentSizes();
     testDifferentHashCodes();
   }
 
   static void testThrows(Iterator<int> it) {
     Expect.equals(false, it.hasNext());
     var exception = null;
     try {
       it.next();
-    } catch (NoMoreElementsException e) {
+    } on NoMoreElementsException catch (e) {
       exception = e;
     }
     Expect.equals(true, exception != null);
   }
 
   static int sum(int expected, Iterator<int> it) {
     int count = 0;
     while (it.hasNext()) {
       count += it.next();
     }
@@ skipping 102 matching lines @@
         Expect.equals(true, x === element);
       }
       Expect.equals(true, foundIt);
     }
   }
 }
 
 main() {
   SetIteratorTest.testMain();
 }