Prepare for decoupling analyzer ASTs from element model.

pkg/dev_compiler/lib/src/compiler/source_map_printer.dart

 // Copyright (c) 2015, 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.
 
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/resolution_accessors.dart';
 import 'package:source_maps/source_maps.dart' hide Printer;
 import 'package:source_span/source_span.dart' show SourceLocation;
 
 import '../js_ast/js_ast.dart' as JS;
 
 class SourceMapPrintingContext extends JS.SimpleJavaScriptPrintingContext {
   /// Current line in the buffer;
   int _line = 0;
 
   /// Current column in the buffer.
@@ skipping 25 matching lines @@
 
   void enterNode(JS.Node jsNode) {
     AstNode node = jsNode.sourceInformation;
     if (node == null || node.offset == -1) return;
     if (unit == null) {
       // This is a top-level declaration.  Note: consecutive top-level
       // declarations may come from different compilation units due to
       // parts.
       _currentTopLevelDeclaration = node;
       unit = node.getAncestor((n) => n is CompilationUnit);
-      sourcePath = unit.element.source.fullName;
+      sourcePath = elementForCompilationUnit(unit).source.fullName;
     }
 
     _mark(node.offset, _getIdentifier(node));
   }
 
   void exitNode(JS.Node jsNode) {
     AstNode node = jsNode.sourceInformation;
     if (unit == null || node == null || node.offset == -1) return;
 
     // TODO(jmesserly): in many cases marking the end will be unnecessary.
@@ skipping 17 matching lines @@
             sourceUrl: sourcePath,
             line: loc.lineNumber - 1,
             column: loc.columnNumber - 1),
         new SourceLocation(buffer.length, line: _line, column: _column),
         identifier);
   }
 }
 
 const int _LF = 10;
 const int _CR = 13;