Revert "Move dart2js from sdk/lib/_internal/compiler to pkg/compiler"

pkg/analyzer2dart/lib/src/tree_shaker.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 analyzer2dart.treeShaker;
 
 import 'dart:collection';
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/source.dart';
-import 'package:compiler/src/universe/universe.dart';
+import 'package:compiler/implementation/universe/universe.dart';
 
 import 'closed_world.dart';
 import 'util.dart';
 import 'semantic_visitor.dart';
 import 'identifier_semantics.dart';
 
 /**
  * The result of performing local reachability analysis on a method.
  */
 class MethodAnalysis {
@@ skipping 365 matching lines @@
     // null, because that would have been detected by the analyzer and
     // reported as a compile time error.
     analysis.calls.add(node.staticElement);
   }
 
   @override
   void handleAssignmentExpression(AssignmentExpression node) {
     // Don't special-case assignment expressions.
   }
 }