Fix ContextBuilderImplTest on Windows.

TBR

R=brianwilkerson@google.com

Change-Id: Id21b8756e6cb097d042bfc492b1f67822165c4c4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/207222
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
diff --git a/pkg/analyzer/test/src/dart/analysis/context_builder_test.dart b/pkg/analyzer/test/src/dart/analysis/context_builder_test.dart
index 5c75695..f0a3fd2 100644
--- a/pkg/analyzer/test/src/dart/analysis/context_builder_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/context_builder_test.dart
@@ -218,7 +218,7 @@
       resourceProvider: resourceProvider,
     ).createContext(
       contextRoot: roots.single,
-      sdkPath: sdkRoot,
+      sdkPath: convertPath(sdkRoot),
     );
   }