Enabling adding and querying for source maps in a MappingBundle.

lib/parser.dart

Index: lib/parser.dart
diff --git a/lib/parser.dart b/lib/parser.dart
index 1c2318774a2c5691d68c74f258096cf6d322243a..3b65e89109d63a388ad7e7e4e7656899286f701b 100644
--- a/lib/parser.dart
+++ b/lib/parser.dart
@@ -180,16 +180,20 @@ class MultiSectionMapping extends Mapping {
 class MappingBundle extends Mapping {
   Map<String, SingleMapping> _mappings = {};
 
+  MappingBundle() {}
+
   MappingBundle.fromJson(List json, {String mapUrl}) {
     for (var map in json) {
-      var mapping = parseJson(map, mapUrl: mapUrl) as SingleMapping;
-      var targetUrl = mapping.targetUrl;
-      // TODO(jacobr): verify that targetUrl is valid uri instead of a windows
-      // path.
-      _mappings[targetUrl] = mapping;
+      addMapping(parseJson(map, mapUrl: mapUrl) as SingleMapping);
     }
   }
 
+  addMapping(SingleMapping mapping) {
+    // TODO(jacobr): verify that targetUrl is valid uri instead of a windows
+    // path.
+    _mappings[mapping.targetUrl] = mapping;
+  }
+
   /// Encodes the Mapping mappings as a json map.
   List toJson() => _mappings.values.map((v) => v.toJson()).toList();
 
@@ -201,6 +205,8 @@ class MappingBundle extends Mapping {
     return buff.toString();
   }
 
+  bool containsMapping(String url) => _mappings.containsKey(url);
+
   SourceMapSpan spanFor(int line, int column,
       {Map<String, SourceFile> files, String uri}) {
     if (uri == null) {