When addSource() in tests, call both addFile() and changeFile().

pkg/analysis_server/test/abstract_context.dart

Index: pkg/analysis_server/test/abstract_context.dart
diff --git a/pkg/analysis_server/test/abstract_context.dart b/pkg/analysis_server/test/abstract_context.dart
index 6b9a5aed3047df5ae8ebb7a6161fda9db8f3f72d..e3c4b93508e4d74bdf0e32d153e602c63efb2595 100644
--- a/pkg/analysis_server/test/abstract_context.dart
+++ b/pkg/analysis_server/test/abstract_context.dart
@@ -86,6 +86,7 @@ class AbstractContextTest {
     File file = newFile(path, content);
     if (enableNewAnalysisDriver) {
       driver.addFile(path);
+      driver.changeFile(path);

[Brian Wilkerson, 2017/02/09 16:43:54]

Should `addFile` be extended to also always do the work done by `changeFile`, or
are there places where it makes sense so call `addFile` without calling
`changeFile`?

[scheglov, 2017/02/09 16:48:03]

In general - no.
We just allow us to be a bit sloppy in tests.

       _fileContentOverlay[path] = content;
       return null;
     } else {