Add KernelWorldBuilder and KElement model.

pkg/compiler/lib/src/compiler.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.
 
 library dart2js.compiler_base;
 
 import 'dart:async' show EventSink, Future;
 
 import '../compiler_new.dart' as api;
 import 'cache_strategy.dart' show CacheStrategy;
@@ skipping 1541 matching lines @@
       return spanFromTokens(node, node);
     } else if (node is HInstruction) {
       return spanFromHInstruction(node);
     } else if (node is Element) {
       return spanFromElement(node);
     } else if (node is MetadataAnnotation) {
       return node.sourcePosition;
     } else if (node is Local) {
       Local local = node;
       return spanFromElement(local.executableContext);
+    } else if (node is Entity) {
+      return spanFromElement(currentElement);
     } else {
       throw 'No error location.';
     }
   }
 
   Element _elementFromHInstruction(HInstruction instruction) {
     return instruction.sourceElement is Element
         ? instruction.sourceElement
         : null;
   }
@@ skipping 415 matching lines @@
   _ElementScanner(this.scanner);
   void scanLibrary(LibraryElement library) => scanner.scanLibrary(library);
   void scanUnit(CompilationUnitElement unit) => scanner.scan(unit);
 }
 
 class _EmptyEnvironment implements Environment {
   const _EmptyEnvironment();
 
   String valueOf(String key) => null;
 }