cros: Minor issues regarding submit button and tabbing on user pod fixed.

ui/login/account_picker/user_pod_template.html

 <dom-module id="user-pod-template-shared-styles">
   <template>
     <link rel="stylesheet" href="user_pod_template.css">
   </template>
 </dom-module>
 
 <style is="custom-style" include="user-pod-template-shared-styles"></style>
 
 <iron-iconset-svg name="user-pod" size="24">
   <svg>
@@ skipping 37 matching lines @@
         <div class="password-container">
           <input type="password" class="password"
                  i18n-values="placeholder:passwordHint">
         </div>
 <if expr="chromeos">
         <div class="capslock-hint-container">
           <img class="capslock-hint"
                src="chrome://theme/IDR_LOGIN_PASSWORD_CAPS_LOCK" alt>
         </div>
         <paper-icon-button class="submit-button" disabled
-                           icon="user-pod:arrow-forward">
+                           icon="user-pod:arrow-forward" tabindex="-1">
         </paper-icon-button>
 </if>
       </div>
       <!-- User Click Authentication -->
       <div class="password-label"></div>
       <div class="signin-transition-container">
         <span class="signing-in-label" i18n-content="signingIn"></span>
         <span class="animated-ellipsis-component0">.</span>
         <span class="animated-ellipsis-component1">.</span>
         <span class="animated-ellipsis-component2">.</span>
@@ skipping 121 matching lines @@
              i18n-content="publicSessionLanguageAndInput"></a>
         </div>
         <button class="enter-button"
                 i18n-content="publicAccountEnter"
                 i18n-values="aria-label:publicAccountEnterAccessibleName">
         </button>
       </div>
     </div>
   </div>
 </div>