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

pkg/front_end/lib/src/base/source.dart

Index: pkg/front_end/lib/src/base/source.dart
diff --git a/pkg/front_end/lib/src/base/source.dart b/pkg/front_end/lib/src/base/source.dart
index 0ed4747915f61d9d45bc041f720f635fe9cb7486..e20a0345d88c31b7c34190bd59c75b21dd776755 100644
--- a/pkg/front_end/lib/src/base/source.dart
+++ b/pkg/front_end/lib/src/base/source.dart
@@ -5,6 +5,7 @@
 import 'package:front_end/src/base/analysis_target.dart';
 import 'package:front_end/src/base/timestamped_data.dart';
 import 'package:front_end/src/base/uri_kind.dart';
+import 'package:source_span/source_span.dart' as source_span;
 
 /**
  * The interface `Source` defines the behavior of objects representing source code that can be
@@ -107,6 +108,11 @@ abstract class Source implements AnalysisTarget {
   Source get source => this;
 
   /**
+   * Return the [source_span.SourceFile] object corresponding to this source.
+   */
+  source_span.SourceFile get sourceFile;
+
+  /**
    * Return the URI from which this source was originally derived.
    *
    * @return the URI from which this source was originally derived