feat(compiler): allow setting attributes on a host element

Closes #1402

modules/angular2/src/dom/browser_adapter.dart

@@ -248,6 +248,9 @@ class BrowserDomAdapter extends GenericBrowserDomAdapter {
     return new Map.from(element.attributes);
   }
 
+  bool hasAttribute(Element element, String attribute) =>
+      element.attributes.containsKey(attribute);
+
   String getAttribute(Element element, String attribute) =>
       element.getAttribute(attribute);
 

modules/angular2/src/dom/browser_adapter.es6

@@ -263,6 +263,9 @@ export class BrowserDomAdapter extends GenericBrowserDomAdapter {
     }
     return res;
   }
+  hasAttribute(element, attribute:string) {
+    return element.hasAttribute(attribute);
+  }
   getAttribute(element, attribute:string) {
     return element.getAttribute(attribute);
   }

modules/angular2/src/dom/dom_adapter.js

@@ -199,6 +199,9 @@ export class DomAdapter {
   attributeMap(element) {
     throw _abstract();
   }
+  hasAttribute(element, attribute:string):boolean {
+    throw _abstract();
+  }
   getAttribute(element, attribute:string):string {
     throw _abstract();
   }

modules/angular2/src/dom/html_adapter.dart

@@ -211,6 +211,9 @@ class Html5LibDomAdapter implements DomAdapter {
     });
     return map;
   }
+  hasAttribute(element, String attribute) {
+    throw 'not implemented';
+  }
   getAttribute(element, String attribute) {
     throw 'not implemented';
   }

modules/angular2/src/dom/parse5_adapter.cjs

@@ -384,6 +384,9 @@ export class Parse5DomAdapter extends DomAdapter {
     }
     return res;
   }
+  hasAttribute(element, attribute:string) {
+    return element.attribs && element.attribs.hasOwnProperty(attribute);
+  }
   getAttribute(element, attribute:string) {
     return element.attribs && element.attribs.hasOwnProperty(attribute)? element.attribs[attribute]: null;
   }