Add source mappings and inlined Dart code to diff_view.

tests/compiler/dart2js/sourcemaps/sourcemap_helper.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 sourcemap.helper;
 
 import 'dart:async';
 import 'dart:io';
 import 'package:compiler/compiler_new.dart';
 import 'package:compiler/src/apiimpl.dart' as api;
@@ skipping 370 matching lines @@
       new JavaScriptTracer(codePositions, [visitor]).apply(node);
       List<CodePoint> codePoints = visitor.codePoints;
       mainSourceMapInfo = new SourceMapInfo(
           null, code, node,
           codePoints,
           codePositions,
           nodeMap);
     }
 
     return new SourceMaps(
-        sourceFileManager, mainSourceMapInfo, elementSourceMapInfos);
+        compiler,
+        sourceFileManager,
+        mainSourceMapInfo,
+        elementSourceMapInfos);
   }
 }
 
 class SourceMaps {
+  final api.CompilerImpl compiler;
   final SourceFileManager sourceFileManager;
   // TODO(johnniwinther): Supported multiple output units.
   final SourceMapInfo mainSourceMapInfo;
   final Map<Element, SourceMapInfo> elementSourceMapInfos;
 
   SourceMaps(
+      this.compiler,
       this.sourceFileManager,
       this.mainSourceMapInfo,
           this.elementSourceMapInfos);
 }
 
 /// Source mapping information for the JavaScript code of an [Element].
 class SourceMapInfo {
   final String name;
   final Element element;
   final String code;
@@ skipping 176 matching lines @@
       absoluteUri = base.resolveUri(uri);
     } else {
       absoluteUri = base.resolve(uri);
     }
     return sourceFiles.putIfAbsent(absoluteUri, () {
       String text = new File.fromUri(absoluteUri).readAsStringSync();
       return new StringSourceFile.fromUri(absoluteUri, text);
     });
   }
 }