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

pkg/compiler/lib/src/world.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.
 
 part of dart2js;
 
 abstract class ClassWorld {
   // TODO(johnniwinther): Refine this into a `BackendClasses` interface.
   Backend get backend;
 
@@ skipping 504 matching lines @@
     // method of function classes that were generated for function
     // expressions. In such a case, we have to look at the original
     // function expressions's element.
     // TODO(herhut): Generate classes for function expressions earlier.
     if (element is closureMapping.SynthesizedCallMethodElementX) {
       return getMightBePassedToApply(element.expression);
     }
     return functionsThatMightBePassedToApply.contains(element);
   }
 }