Fix more tests under windows

pkg/analyzer/test/src/context/abstract_context.dart

Index: pkg/analyzer/test/src/context/abstract_context.dart
diff --git a/pkg/analyzer/test/src/context/abstract_context.dart b/pkg/analyzer/test/src/context/abstract_context.dart
index b497c52963f84796b50ddeac0f6878f45ad9225c..ae77652365453185dffc33eb84c336409a5dda0e 100644
--- a/pkg/analyzer/test/src/context/abstract_context.dart
+++ b/pkg/analyzer/test/src/context/abstract_context.dart
@@ -126,7 +126,8 @@ class AbstractContextTest {
   DartSdk createDartSdk() => new MockSdk(resourceProvider: resourceProvider);
 
   Source newSource(String path, [String content = '']) {
-    File file = resourceProvider.newFile(path, content);
+    File file =
+        resourceProvider.newFile(resourceProvider.convertPath(path), content);
     return file.createSource();
   }