Add Platform.packageRoot and Platform.executableArguments to dart:io.

sdk/lib/_internal/lib/io_patch.dart

Index: sdk/lib/_internal/lib/io_patch.dart
diff --git a/sdk/lib/_internal/lib/io_patch.dart b/sdk/lib/_internal/lib/io_patch.dart
index e41a2ce63e58d11cfe4b6f7ddf0bf3f1b4bbe629..4216317a3381784cef11b8c45e92851893c9f9f3 100644
--- a/sdk/lib/_internal/lib/io_patch.dart
+++ b/sdk/lib/_internal/lib/io_patch.dart
@@ -163,7 +163,13 @@ patch class _Platform {
     throw new UnsupportedError("Platform._localHostname");
   }
   patch static _executable() {
-    throw new UnsupportedError("Platform_Executable");
+    throw new UnsupportedError("Platform._executable");
+  }
+  patch static List<String> _executableArguments() {
+    throw new UnsupportedError("Platform._executableArguments");
+  }
+  patch static String _packageRoot() {
+    throw new UnsupportedError("Platform._packageRoot");
   }
   patch static _environment() {
     throw new UnsupportedError("Platform._environment");