Don't add sources to DartSdk contexts.

pkg/analyzer/lib/src/generated/sdk_io.dart

Index: pkg/analyzer/lib/src/generated/sdk_io.dart
diff --git a/pkg/analyzer/lib/src/generated/sdk_io.dart b/pkg/analyzer/lib/src/generated/sdk_io.dart
index ae1512ff82c58b2dfa5ca374bd691ab773fd93ba..a50eb9598b71a160df02f2a9e8cd509ae7784f0b 100644
--- a/pkg/analyzer/lib/src/generated/sdk_io.dart
+++ b/pkg/analyzer/lib/src/generated/sdk_io.dart
@@ -258,19 +258,12 @@ class DirectoryBasedDartSdk implements DartSdk {
       _analysisContext = new SdkAnalysisContext();
       SourceFactory factory = new SourceFactory([new DartUriResolver(this)]);
       _analysisContext.sourceFactory = factory;
-      List<String> uris = this.uris;
       // Try to use summaries.
       SdkBundle sdkBundle = _getSummarySdkBundle();
       if (sdkBundle != null) {
         _analysisContext.resultProvider =
             new SdkSummaryResultProvider(_analysisContext, sdkBundle);
       }
-      // Add sources.
-      ChangeSet changeSet = new ChangeSet();
-      for (String uri in uris) {
-        changeSet.addedSource(factory.forUri(uri));
-      }
-      _analysisContext.applyChanges(changeSet);
     }
     return _analysisContext;
   }