Connect analyzer's AnalysisError object to front_end's CompilationError.

pkg/analyzer/lib/src/string_source.dart

Index: pkg/analyzer/lib/src/string_source.dart
diff --git a/pkg/analyzer/lib/src/string_source.dart b/pkg/analyzer/lib/src/string_source.dart
index ce0c08777749b715cc38db44610380199cdc896a..987e8985ea0ccd3686ad6c1e491a274b35313b46 100644
--- a/pkg/analyzer/lib/src/string_source.dart
+++ b/pkg/analyzer/lib/src/string_source.dart
@@ -6,6 +6,7 @@ library analyzer.src.string_source;
 
 import 'package:analyzer/src/generated/engine.dart' show TimestampedData;
 import 'package:analyzer/src/generated/source.dart';
+import 'package:source_span/source_span.dart' as source_span;
 
 /**
  * An implementation of [Source] that's based on an in-memory Dart string.
@@ -16,6 +17,8 @@ class StringSource extends Source {
    */
   final String _contents;
 
+  source_span.SourceFile _sourceFile;
+
   @override
   final String fullName;
 
@@ -47,6 +50,10 @@ class StringSource extends Source {
   String get shortName => fullName;
 
   @override
+  source_span.SourceFile get sourceFile =>
+      _sourceFile ??= new source_span.SourceFile(_contents, url: uri);
+
+  @override
   UriKind get uriKind => UriKind.FILE_URI;
 
   /**