Don't add sources to DartSdk contexts.

pkg/analysis_server/test/mock_sdk.dart

Index: pkg/analysis_server/test/mock_sdk.dart
diff --git a/pkg/analysis_server/test/mock_sdk.dart b/pkg/analysis_server/test/mock_sdk.dart
index 1fbb426be7a7582604bc7dc6ade9970fb6b85c2c..c43ef63e962da8c60a33f7b4d2bb2d507ef7f529 100644
--- a/pkg/analysis_server/test/mock_sdk.dart
+++ b/pkg/analysis_server/test/mock_sdk.dart
@@ -222,12 +222,6 @@ external void printToConsole(String line);
       _analysisContext = new SdkAnalysisContext();
       SourceFactory factory = new SourceFactory([new DartUriResolver(this)]);
       _analysisContext.sourceFactory = factory;
-      ChangeSet changeSet = new ChangeSet();
-      for (String uri in uris) {
-        Source source = factory.forUri(uri);
-        changeSet.addedSource(source);
-      }
-      _analysisContext.applyChanges(changeSet);
     }
     return _analysisContext;
   }