Compute the script Uri lazily

pkg/dev_compiler/tool/input_sdk/patch/io_patch.dart

Index: pkg/dev_compiler/tool/input_sdk/patch/io_patch.dart
diff --git a/pkg/dev_compiler/tool/input_sdk/patch/io_patch.dart b/pkg/dev_compiler/tool/input_sdk/patch/io_patch.dart
index afd48e5e738b30416267a4a19dd203ca90eaccfb..31cfd05739b7f268d3ffbc3b77754f2587114c40 100644
--- a/pkg/dev_compiler/tool/input_sdk/patch/io_patch.dart
+++ b/pkg/dev_compiler/tool/input_sdk/patch/io_patch.dart
@@ -255,6 +255,11 @@ class _Platform {
   static String _localeName() {
     throw new UnsupportedError("Platform._localeName");
   }
+
+  @patch
+  static Uri _script() {
+    throw new UnsupportedError("Platform._script");
+  }
 }
 
 @patch