Fixes for context_manager_test on Windows.

pkg/analyzer/lib/source/config.dart

Index: pkg/analyzer/lib/source/config.dart
diff --git a/pkg/analyzer/lib/source/config.dart b/pkg/analyzer/lib/source/config.dart
index 0ca954a8f4f066498f341cfac5995be796adbe5d..db44b4eec4b6b87b01495da59ffcbc6895b5b6d4 100644
--- a/pkg/analyzer/lib/source/config.dart
+++ b/pkg/analyzer/lib/source/config.dart
@@ -91,7 +91,8 @@ class PubspecConfiguration extends AnalysisConfiguration {
               Uri pragma = new Uri.file('config/${descriptor.pragma}.yaml',
                   windows: false);
               Uri optionsUri = uri.resolveUri(pragma);
-              File file = resourceProvider.getFile(optionsUri.toFilePath());
+              String path = resourceProvider.pathContext.fromUri(optionsUri);
+              File file = resourceProvider.getFile(path);
               if (file.exists) {
                 return optionsProvider.getOptionsFromFile(file);
               }