fixes #6, refactor to use AnalysisError/Listener throughout dev_compiler

lib/src/codegen/js_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.
 
 library dev_compiler.src.codegen.js_printer;
 
 import 'dart:io' show Directory, File;
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:path/path.dart' as path;
 import 'package:source_maps/source_maps.dart' as srcmaps show Printer;
@@ skipping 66 matching lines @@
     if (name != null) {
       // TODO(jmesserly): mark only uses the beginning of the span, but
       // we're required to pass this as a valid span.
       var end = _location(node.end);
       printer.mark(new SourceMapSpan(loc, end, name, isIdentifier: true));
     } else {
       printer.mark(loc);
     }
   }
 
-  SourceLocation _location(int offset) => locationForOffset(unit, uri, offset);
+  SourceLocation _location(int offset) =>
+      locationForOffset(unit.lineInfo, uri, offset);
 
   Uri _makeRelativeUri(Uri src) {
     return new Uri(path: path.relative(src.path, from: outputDir));
   }
 
   void exitNode(JS.Node jsNode) {
     AstNode node = jsNode.sourceInformation;
     if (node is CompilationUnit) {
       unit = null;
       uri = null;
       return;
     }
     if (unit == null || node == null || node.offset == -1) return;
 
     // TODO(jmesserly): in many cases marking the end will be unnecessary.
     printer.mark(_location(node.end));
   }
 
   String _getIdentifier(AstNode node) {
     if (node is SimpleIdentifier) return node.name;
     return null;
   }
 }