Remove unused import and make Makefile more flexible

dart/sdk/lib/_internal/compiler/implementation/deferred_load.dart

 // Copyright (c) 2014, 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 deferred_load;
 
 import 'constants/expressions.dart';
 
 import 'dart2jslib.dart' show
     Backend,
@@ skipping 40 matching lines @@
     LibraryDependency,
     LiteralString,
     LiteralDartString;
 
 import 'tree/tree.dart' as ast;
 
 import 'resolution/resolution.dart' show
     TreeElements,
     AnalyzableElementX;
 
-import "dart:math" show min;
-
 /// A "hunk" of the program that will be loaded whenever one of its [imports]
 /// are loaded.
 ///
 /// Elements that are only used in one deferred import, is in an OutputUnit with
 /// the deferred import as single element in the [imports] set.
 ///
 /// Whenever a deferred Element is shared between several deferred imports it is
 /// in an output unit with those imports in the [imports] Set.
 ///
 /// OutputUnits are equal if their [imports] are equal.
@@ skipping 683 matching lines @@
     Element maybePrefix = elements[identifier];
     if (maybePrefix != null && maybePrefix.isPrefix) {
       PrefixElement prefixElement = maybePrefix;
       if (prefixElement.isDeferred) {
         return prefixElement;
       }
     }
     return null;
   }
 }