Generate and use cross frame wrappers for types in other frames/windows.

lib/dom/templates/crossframe_impl.darttemplate

Index: lib/dom/templates/crossframe_impl.darttemplate
diff --git a/lib/dom/templates/crossframe_impl.darttemplate b/lib/dom/templates/crossframe_impl.darttemplate
new file mode 100644
index 0000000000000000000000000000000000000000..22219ec120db82b8c9fd00985d94819527c2c04f
--- /dev/null
+++ b/lib/dom/templates/crossframe_impl.darttemplate
@@ -0,0 +1,22 @@
+
+class _$(NAME)CrossFrameImpl implements $(NAME) {
+$!MEMBERS
+  // Implementation.
+  $(CLASSNAME) $POINTER;
+
+  _$(NAME)CrossFrameImpl._(this.$POINTER);
+
+  static _createSafe(ptr) {
+    if (ptr === $LOCAL) {
+      return $LOCAL;
+    } else {
+      // TODO(vsm): Should we cache to try to get reference equality?
+      return new _$(NAME)CrossFrameImpl._(ptr);
+    }
+  }
+
+  operator ==(other) {
+    return (other is _$(NAME)CrossFrameImpl) &&
+           (this.$POINTER === other.$POINTER);
+  }
+}