fix(force_auth): mention service name in force_auth

Fixes #4928

Author: vladikoff

app/scripts/templates/force_auth.mustache

@@ -1,6 +1,14 @@
 <div id="main-content" class="card">
   <header>
-    <h1 id="fxa-force-auth-header">{{#t}}Sign in to continue{{/t}}</h1>
+    <h1 id="fxa-force-auth-header">
+      {{#serviceName}}
+        <!-- L10N: For languages structured like English, the second phrase can read "to continue to %(serviceName)s" -->
+        {{#t}}Sign in{{/t}} <span class="service">{{#t}}Continue to %(serviceName)s{{/t}}</span>
+      {{/serviceName}}
+      {{^serviceName}}
+        {{#t}}Sign in to continue{{/t}}
+      {{/serviceName}}
+    </h1>
   </header>
 
   <section>

app/scripts/views/force_auth.js

@@ -10,6 +10,7 @@ import FormView from './form';
 import NullBehavior from './behaviors/null';
 import PasswordResetMixin from './mixins/password-reset-mixin';
 import SignInView from './sign_in';
+import ServiceMixin from './mixins/service-mixin';
 import Template from 'templates/force_auth.mustache';
 import Transform from '../lib/transform';
 import Vat from '../lib/vat';
@@ -193,7 +194,8 @@ var View = SignInView.extend({
 
 Cocktail.mixin(
   View,
-  PasswordResetMixin
+  PasswordResetMixin,
+  ServiceMixin
 );
 
 module.exports = View;

app/tests/spec/views/force_auth.js

@@ -172,11 +172,29 @@ define(function (require, exports, module) {
           assert.isFalse(view.navigate.called);
         });
 
+        it('has no service name', function () {
+          assert.lengthOf(view.$('.service'), 0);
+        });
+
         it('does not error', function () {
           assert.lengthOf(view.$('.error.visible'), 0);
         });
       });
 
+      describe('with service=sync', function () {
+        it('has the service title', function () {
+
+          relier.set({
+            serviceName: 'Firefox Sync',
+            uid: TestHelpers.createUid()
+          });
+
+          return view.render().then(() => {
+            assert.equal(view.$('.service').text(), 'Continue to Firefox Sync');
+          });
+        });
+      });
+
       describe('with registered email, unregistered uid', function () {
         beforeEach(function () {
           relier.set({