Complain about use before declaration.

sdk/lib/js/dart2js/js_dart2js.dart

 // Copyright (c) 2013, 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.
 
 /**
  * Support for interoperating with JavaScript.
  *
  * This library provides access to JavaScript objects from Dart, allowing
  * Dart code to get and set properties, and call methods of JavaScript objects
  * and invoke JavaScript functions. The library takes care of converting
@@ skipping 482 matching lines @@
     return callMethod('pop');
   }
 
   void removeRange(int start, int end) {
     _checkRange(start, end, length);
     callMethod('splice', [start, end - start]);
   }
 
   void setRange(int start, int end, Iterable<E> iterable, [int skipCount = 0]) {
     _checkRange(start, end, length);
-    int length = end - start;
+    length = end - start;
     if (length == 0) return;
     if (skipCount < 0) throw new ArgumentError(skipCount);
     var args = [start, length]..addAll(iterable.skip(skipCount).take(length));
     callMethod('splice', args);
   }
 
   void sort([int compare(E a, E b)]) {
     // Note: arr.sort(null) is a type error in FF
     callMethod('sort', compare == null ? [] : [compare]);
   }
@@ skipping 205 matching lines @@
 Function allowInteropCaptureThis(Function f) {
   if (JS('bool', 'typeof(#) == "function"', f)) {
     // Behavior when the function is already a JS function is unspecified.
     throw new ArgumentError(
         "Function is already a JS function so cannot capture this.");
     return f;
   } else {
     return _convertDartFunctionFastCaptureThis(f);
   }
 }