Be more strict about attributes in sky-binder.

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

Index: sky/framework/sky-element/element-registry.sky
diff --git a/sky/framework/sky-element/element-registry.sky b/sky/framework/sky-element/element-registry.sky
index 8af18534585bdf73d9fc6d40e9650b3b9c960ef3..a38f22b37fe358a666efc46a89aa64305689d0a1 100644
--- a/sky/framework/sky-element/element-registry.sky
+++ b/sky/framework/sky-element/element-registry.sky
@@ -7,33 +7,15 @@
 <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',
-  'style',
   'tabindex',
-  'title',
-  'type',
-  'width',
+  'style',
 ]);
 
 var attributeConverters = {
@@ -76,7 +58,7 @@ class ElementRegistration {
   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;
@@ -119,10 +101,13 @@ class ElementRegistration {
 
 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;
 }
@@ -135,11 +120,43 @@ 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,