Update top_level_prefixed_library_test.lib library name.
Update top_level_prefixed_library_test.lib library name.

The following error was reported on bots with the new analysis driver,
but it was not reported before, because DartWorkManager.getErrors()
skips non-Dart sources.

WARNING|STATIC_WARNING|PART_OF_DIFFERENT_LIBRARY|/b/build/slave/azr-be/build/sdk/tests/language/top_level_prefixed_library_test.lib|6|6|22|Expected this library to be part of 'TopLevelPrefixedLibrary', not 'TopLevelMultipleFilesTest.dart'.

The test does not state its intentions, so I did my best guess and
fixed the library name.

R=hausner@google.com, brianwilkerson@google.com
BUG=

Review-Url: https://codereview.chromium.org/2691903007 .

dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk