Fix various warnings from the analyzer.

sdk/lib/json/json.dart

Index: sdk/lib/json/json.dart
diff --git a/sdk/lib/json/json.dart b/sdk/lib/json/json.dart
index e85d93fa8f5a7f7afeb0fb2dda0c8479c982e179..4348767eea666865b422cd6e22b80c4042b1f1bc 100644
--- a/sdk/lib/json/json.dart
+++ b/sdk/lib/json/json.dart
@@ -507,7 +507,7 @@ class JsonParser {
         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++) {
@@ -530,7 +530,6 @@ class JsonParser {
           }
           char = value;
           break;
-        }
         default:
           if (char < SPACE) fail(position, "Control character in string");
           fail(position, "Unrecognized string escape");