Deprecate publicly-visible properties on Style in path.

pkg/path/lib/src/context.dart

Index: pkg/path/lib/src/context.dart
diff --git a/pkg/path/lib/src/context.dart b/pkg/path/lib/src/context.dart
index 88ca61fa5eee43d2478fd5f68616c3261d55fd0f..f3826d78c6c307fe23c84184aea9f22e7b7751f2 100644
--- a/pkg/path/lib/src/context.dart
+++ b/pkg/path/lib/src/context.dart
@@ -4,6 +4,7 @@
 
 library path.context;
 
+import 'internal_style.dart';
 import 'style.dart';
 import 'parsed_path.dart';
 import 'path_exception.dart';
@@ -30,7 +31,12 @@ class Context {
       }
     }
 
-    if (style == null) style = Style.platform;
+    if (style == null) {
+      style = Style.platform;
+    } else if (style is! InternalStyle) {
+      throw new ArgumentError("Only styles defined by the path package are "
+          "allowed.");
+    }
 
     return new Context._(style, current);
   }
@@ -38,7 +44,7 @@ class Context {
   Context._(this.style, this.current);
 
   /// The style of path that this context works with.
-  final Style style;
+  final InternalStyle style;
 
   /// The current directory that relative paths will be relative to.
   final String current;