fix(autocomplete): adds tabindex support for autocomplete

Closes #2113

src/components/autocomplete/js/autocompleteDirective.js

@@ -150,12 +150,17 @@ function MdAutocomplete () {
     template:     function (element, attr) {
       var noItemsTemplate = getNoItemsTemplate(),
           itemTemplate    = getItemTemplate(),
-          leftover        = element.html();
+          leftover        = element.html(),
+          tabindex        = attr.tabindex;
 
       if (noItemsTemplate) {
         hasNotFoundTemplate = true;
       }
 
+      if (attr.hasOwnProperty('tabindex')) {
+        element.attr('tabindex', '-1');
+      }
+
       return '\
         <md-autocomplete-wrap\
             layout="row"\
@@ -216,6 +221,7 @@ function MdAutocomplete () {
             <md-input-container flex ng-if="floatingLabel">\
               <label>{{floatingLabel}}</label>\
               <input type="search"\
+                  ' + (tabindex != null ? 'tabindex="' + tabindex + '"' : '') + '\
                   id="{{ inputId || \'fl-input-\' + $mdAutocompleteCtrl.id }}"\
                   name="{{inputName}}"\
                   autocomplete="off"\
@@ -238,6 +244,7 @@ function MdAutocomplete () {
         } else {
           return '\
             <input flex type="search"\
+                ' + (tabindex != null ? 'tabindex="' + tabindex + '"' : '') + '\
                 id="{{ inputId || \'input-\' + $mdAutocompleteCtrl.id }}"\
                 name="{{inputName}}"\
                 ng-if="!floatingLabel"\