Moved RuntimeOptions from coreimpl to core, renamed to _OptionsImpl.

lib/core/options.dart

Index: lib/core/options.dart
diff --git a/lib/core/options.dart b/lib/core/options.dart
index 0685d176f5b0cc8f5486485ed29863f4ac9254c2..3377c30d2eaf56ca0d53cbd6e31c188615ddadc8 100644
--- a/lib/core/options.dart
+++ b/lib/core/options.dart
@@ -13,7 +13,7 @@ abstract class Options {
    * A newly constructed Options object contains the arguments exactly as they
    * have been passed to the isolate.
    */
-  factory Options() => new RuntimeOptions();
+  factory Options() => new _OptionsImpl();
 
   /**
    * Returns a list of arguments that have been passed to this isolate. Any
@@ -42,3 +42,32 @@ abstract class Options {
    */
   String get script;
 }
+
+class _OptionsImpl implements Options {
+  List<String> get arguments {
+    if (_arguments === null) {
+      // On first access make a copy of the native arguments.
+      _arguments = _nativeArguments.getRange(0, _nativeArguments.length);
+    }
+    return _arguments;
+  }
+
+  String get executable {
+    return _nativeExecutable;
+  }
+
+  String get script {
+    return _nativeScript;
+  }
+
+  List<String> _arguments = null;
+
+  // This arguments singleton is written to by the embedder if applicable.
+  static List<String> _nativeArguments = const [];
+
+  // This executable singleton is written to by the embedder if applicable.
+  static String _nativeExecutable = '';
+
+  // This script singleton is written to by the embedder if applicable.
+  static String _nativeScript = '';
+}