ignore errors deleting the analysis driver cache.

pkg/analysis_server/benchmark/benchmarks.dart

Index: pkg/analysis_server/benchmark/benchmarks.dart
diff --git a/pkg/analysis_server/benchmark/benchmarks.dart b/pkg/analysis_server/benchmark/benchmarks.dart
index aed89bbe452f1fe853c145b69d44c0672af4cbe5..bfc24daad3e0e4f1e2fc3ed4f91ce8e4a7752474 100644
--- a/pkg/analysis_server/benchmark/benchmarks.dart
+++ b/pkg/analysis_server/benchmark/benchmarks.dart
@@ -225,5 +225,11 @@ void deleteServerCache() {
   // ~/.dartServer/.analysis-driver/
   ResourceProvider resourceProvider = PhysicalResourceProvider.INSTANCE;
   Folder stateLocation = resourceProvider.getStateLocation('.analysis-driver');
-  stateLocation.delete();
+  try {
+    if (stateLocation.exists) {
+      stateLocation.delete();
+    }
+  } catch (e) {
+    // ignore any exception
+  }
 }