Registration-based approach to cross frame support.

pkg/dev_compiler/tool/input_sdk/lib/html/dart2js/html_dart2js.dart

Index: pkg/dev_compiler/tool/input_sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/pkg/dev_compiler/tool/input_sdk/lib/html/dart2js/html_dart2js.dart b/pkg/dev_compiler/tool/input_sdk/lib/html/dart2js/html_dart2js.dart
index c2dc6ad20aebb10821fbff56209669d4b5d27415..4309803236d6a01f994c0cf3724f397906411422 100644
--- a/pkg/dev_compiler/tool/input_sdk/lib/html/dart2js/html_dart2js.dart
+++ b/pkg/dev_compiler/tool/input_sdk/lib/html/dart2js/html_dart2js.dart
@@ -63,7 +63,8 @@ import 'dart:_js_helper'
         ForceInline,
         findDispatchTagForInterceptorClass,
         setNativeSubclassDispatchRecord,
-        makeLeafDispatchRecord;
+        makeLeafDispatchRecord,
+        registerGlobalObject;

[vsm, 2017/07/19 15:59:02]

Note, this is just a direct copy now of the dart2js version of this file. 
Forgot to copy over in my last CL (where I added the hook).

 import 'dart:_interceptors'
     show
         Interceptor,
@@ -4301,15 +4302,11 @@ class CssStyleDeclaration extends Interceptor with CssStyleDeclarationBase {
   /// Please note the property name uses camelCase, not-hyphens.
   String getPropertyValue(String propertyName) {
     var propValue = _getPropertyValueHelper(propertyName);
-    return propValue != null ? propValue : '';
+    return propValue ?? '';
   }
 
   String _getPropertyValueHelper(String propertyName) {
-    if (_supportsProperty(_camelCase(propertyName))) {
-      return _getPropertyValue(propertyName);
-    } else {
-      return _getPropertyValue(Device.cssPrefix + propertyName);
-    }
+    return _getPropertyValue(_browserPropertyName(propertyName));
   }
 
   /**
@@ -4322,7 +4319,7 @@ class CssStyleDeclaration extends Interceptor with CssStyleDeclarationBase {
    */
   bool supportsProperty(String propertyName) {
     return _supportsProperty(propertyName) ||
-        _supportsProperty(_camelCase(Device.cssPrefix + propertyName));
+        _supportsProperty(_camelCase("${Device.cssPrefix}$propertyName"));
   }
 
   bool _supportsProperty(String propertyName) {
@@ -4338,15 +4335,23 @@ class CssStyleDeclaration extends Interceptor with CssStyleDeclarationBase {
   String _browserPropertyName(String propertyName) {
     String name = _readCache(propertyName);
     if (name is String) return name;
-    if (_supportsProperty(_camelCase(propertyName))) {
-      name = propertyName;
-    } else {
-      name = Device.cssPrefix + propertyName;
-    }
+    name = _supportedBrowserPropertyName(propertyName);
     _writeCache(propertyName, name);
     return name;
   }
 
+  String _supportedBrowserPropertyName(String propertyName) {
+    if (_supportsProperty(_camelCase(propertyName))) {
+      return propertyName;
+    }
+    var prefixed = "${Device.cssPrefix}$propertyName";
+    if (_supportsProperty(prefixed)) {
+      return prefixed;
+    }
+    // May be a CSS variable, just use it as provided.
+    return propertyName;
+  }
+
   static final _propertyCache = JS('', '{}');
   static String _readCache(String key) =>
       JS('String|Null', '#[#]', _propertyCache, key);
@@ -45868,6 +45873,7 @@ class _DOMWindowCrossFrame implements WindowBase {
       return w;
     } else {
       // TODO(vsm): Cache or implement equality.
+      registerGlobalObject(w);
       return new _DOMWindowCrossFrame(w);
     }
   }