Revert "Dartium JS Interop enabled."

tools/dom/templates/html/impl/impl_Window.darttemplate

Index: tools/dom/templates/html/impl/impl_Window.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_Window.darttemplate b/tools/dom/templates/html/impl/impl_Window.darttemplate
index 36dfc9a7b41f29aa4c35c0917483d9e132ba0949..b119a08ea3bd85b3b5d551054abe0f64149dedf8 100644
--- a/tools/dom/templates/html/impl/impl_Window.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Window.darttemplate
@@ -85,13 +85,13 @@ $if DART2JS
    * Sets the window's location, which causes the browser to navigate to the new
    * location. [value] may be a Location object or a String.
    */
-  set location(value) {
+  void set location(value) {
     _location = value;
   }
 
   // Native getter and setter to access raw Location object.
   dynamic get _location => JS('Location|Null', '#.location', this);
-  set _location(value) {
+  void set _location(value) {
     JS('void', '#.location = #', this, value);
   }
 
@@ -320,7 +320,7 @@ class _BeforeUnloadEvent extends _WrappedEvent implements BeforeUnloadEvent {
 
   String get returnValue => _returnValue;
 
-  set returnValue(String value) {
+  void set returnValue(String value) {
     _returnValue = value;
     // FF and IE use the value as the return value, Chrome will return this from
     // the event callback function.