Clear fast boot rendered head on browser boot

Split initializers into fastboot & browser flavors.

Use placeholder meta tags for marking extent of head.hbs content.

Author: ronco

addon/instance-initializers/head.js

@@ -0,0 +1 @@
+<meta name="ember-cli-head-start" />{{head-content}}<meta name="ember-cli-head-end" />

addon/templates/components/head-layout.hbs

@@ -0,0 +1,7 @@
+import Ember from 'ember';
+import layout from 'ember-cli-head/templates/components/head-layout';
+
+export default Ember.Component.extend({
+  tagName: '',
+  layout
+});

app/components/head-layout.js

@@ -0,0 +1,18 @@
+import Ember from 'ember';
+
+export function initialize(instance) {
+  // clear fast booted head (if any)
+  Ember.$('meta[name="ember-cli-head-start"]')
+    .nextUntil('meta[name="ember-cli-head-end"] ~')
+    .addBack()
+    .remove();
+  const container = instance.lookup ? instance : instance.container;
+  const renderer = container.lookup('renderer:-dom');
+  const component = container.lookup('component:head-layout');
+  component.appendTo(renderer._dom.document.head);
+}
+
+export default {
+  name: 'head-browser',
+  initialize: initialize
+};

app/instance-initializers/browser/head.js

@@ -0,0 +1,20 @@
+export function initialize(instance) {
+  const container = instance.lookup ? instance : instance.container;
+  const renderer = container.lookup('renderer:-dom');
+  const componentFactory =
+          instance._lookupFactory('component:head-layout');
+  // explicitly set renderer & domhelper since we're in fastboot
+  const component = componentFactory.create(
+    instance.ownerInjection(),
+    {
+      renderer,
+      _domHelper: renderer._dom
+    }
+  );
+  component.appendTo(renderer._dom.document.head);
+}
+
+export default {
+  name: 'head-fastboot',
+  initialize: initialize
+};

app/instance-initializers/fastboot/head.js

@@ -0,0 +1,15 @@
+import { moduleForComponent, test } from 'ember-qunit';
+import hbs from 'htmlbars-inline-precompile';
+
+moduleForComponent('head-layout', 'Integration | Component | head layout', {
+  integration: true
+});
+
+test('it renders', function(assert) {
+
+  this.render(hbs`{{head-layout}}`);
+
+  assert.equal(this.$('meta[name="ember-cli-head-start"]').length, 1);
+  assert.equal(this.$('meta[name="ember-cli-head-end"]').length, 1);
+
+});