Fix various warnings from the analyzer.

sdk/lib/json/json.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.
 
 library dart.json;
 
 // JSON parsing and serialization.
 
 /**
  * Error thrown by JSON serialization if an object cannot be serialized.
@@ skipping 489 matching lines @@
       switch (char) {
         case CHAR_b: char = BACKSPACE; break;
         case CHAR_f: char = FORM_FEED; break;
         case CHAR_n: char = NEWLINE; break;
         case CHAR_r: char = CARRIAGE_RETURN; break;
         case CHAR_t: char = TAB; break;
         case SLASH:
         case BACKSLASH:
         case QUOTE:
           break;
-        case CHAR_u: {
+        case CHAR_u:
           int hexStart = position - 1;
           int value = 0;
           for (int i = 0; i < 4; i++) {
             position++;
             if (position == source.length) {
               fail(start - 1, "Unterminated string");
             }
             char = source.charCodeAt(position);
             char -= 0x30;
             if (char < 0) fail(hexStart, "Invalid unicode escape");
             if (char < 10) {
               value = value * 16 + char;
             } else {
               char = (char | 0x20) - 0x31;
               if (char < 0 || char > 5) {
                 fail(hexStart, "Invalid unicode escape");
               }
               value = value * 16 + char + 10;
             }
           }
           char = value;
           break;
-        }
         default:
           if (char < SPACE) fail(position, "Control character in string");
           fail(position, "Unrecognized string escape");
       }
       do {
         chars.add(char);
         position++;
         if (position == source.length) fail(start - 1, "Unterminated string");
         char = source.charCodeAt(position);
         if (char == QUOTE) {
@@ skipping 252 matching lines @@
         first = false;
       });
       sb.add('}');
       seen.removeLast();
       return true;
     } else {
       return false;
     }
   }
 }