Fix SDK partitions leak in tests.

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 d243352bbf40fdbefc18c0ec538510c1ac0bd529..6b9a5aed3047df5ae8ebb7a6161fda9db8f3f72d 100644
--- a/pkg/analysis_server/test/abstract_context.dart
+++ b/pkg/analysis_server/test/abstract_context.dart
@@ -168,6 +168,7 @@ class AbstractContextTest {
   void tearDown() {
     _context = null;
     provider = null;
+    AnalysisEngine.instance.clearCaches();
     AnalysisEngine.instance.logger = null;
   }
 }