Be more strict about attributes in sky-binder.

sky/framework/sky-element/element-registry.sky

 <!--
 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 -->
 <import src="sky-binder.sky" as="binder" />
 <script>
 // TODO(esprehn): It would be nice if these were exposed by the platform so
 // the framework didn't need to hard code a list.
-var defaultAttributesNames = new Set([
-  'accesskey',
-  'alt',
-  'as',
-  'async',
+var globalAttributesNames = new Set([
   'class',
   'contenteditable',
-  'crossorigin',
   'dir',
-  'height',
-  'href',
   'id',
-  'is',
   'lang',
-  'media',
-  'name',
-  'rel',
-  'select',
-  'sizes',
   'spellcheck',
-  'src',
-  'srcset',
+  'tabindex',
   'style',
-  'tabindex',
-  'title',
-  'type',
-  'width',
 ]);
 
 var attributeConverters = {
   boolean: function(value) {
     if (typeof value == 'string')
       return value == 'true';
     return !!value;
   },
   number: function(value) {
     return Number(value);
@@ skipping 22 matching lines @@
     this.tagName = tagName;
     this.attributes = new Map();
     this.eventHandlers = new Map();
     this.template = null;
     Object.preventExtensions(this);
   }
 
   allowsAttribute(name) {
     if (name.startsWith('data-'))
       return true;
-    if (defaultAttributesNames.has(name))
+    if (globalAttributesNames.has(name))
       return true;
     if (this.attributes.has(name))
       return true;
     return false;
   }
 
   defineAttribute(name, type) {
     var converter = attributeConverters[type];
 
     if (!converter) {
@@ skipping 22 matching lines @@
 
   addInstanceEventListeners(instance) {
     for (var eventName of this.eventHandlers.keys()) {
       instance.addEventListener(eventName, eventHandlerCallback);
     }
   }
 }
 
 var registrations = new Map();
 
-function registerElement(tagName) {
+function registerElement(tagName, attributes) {
   if (registrations.has(tagName))
     throw new Error('tagName "' + tagName + '" registered twice.');
   var registration = new ElementRegistration(tagName);
+  for (var name in attributes) {
+    registration.defineAttribute(name, attributes[name]);
+  }
   registrations.set(tagName, registration);
   return registration;
 }
 
 function getRegistration(tagName) {
   return registrations.get(tagName);
 }
 
 function checkAttribute(tagName, attrName) {
   var registration = getRegistration(tagName);
 
   if (!registration)
-    return defaultAttributesNames.has(attrName);
+    return globalAttributesNames.has(attrName);
 
   return registration.allowsAttribute(attrName);
 }
 
+registerElement('img', {
+  'width': 'number',
+  'height': 'number',
+  // TODO(esprehn): Sky probably doesn't want the crossorign attr.
+  'crossorigin': 'string',
+  'src': 'string',
+});
+
+registerElement('import', {
+  'as': 'string',
+  'src': 'string',
+  'async': 'boolean',
+});
+
+registerElement('a', {
+  'href': 'string',
+  'async': 'boolean',
+});
+
+registerElement('content', {
+  'select': 'string',
+});
+
+registerElement('style', {
+  'media': 'string',
+});
+
+registerElement('template', {
+  'if': 'string',
+  'repeat': 'string',
+});
+
 module.exports = {
   registerElement: registerElement,
   getRegistration: getRegistration,
   checkAttribute: checkAttribute,
 };
 </script>