[DEPRECATION] Deprecates old browser support policy

* Adds the deprecation specified in
  https://github.com/emberjs/rfcs/blob/master/text/0685-new-browser-support-policy.md
* Updates the test harness to avoid failing CI for deprecations issued
  on IE11

lib/index.js

@@ -246,6 +246,12 @@ module.exports = {
     let ember;
     let targets = (this.project && this.project.targets && this.project.targets.browsers) || [];
 
+    if (targets.includes('ie 11')) {
+      this.ui.writeWarnLine(
+        'Internet Explorer 11 is listed in your compilation targets, but it will no longer be supported in the next major version of Ember. Please update your targets to remove IE 11 and include new targets that are within the updated support policy. For details on the new browser support policy, see:\n\n - The official documentation: http://emberjs.com/browser-support\n - the deprecation guide: https://emberjs.com/deprecations/v3.x#toc_3-0-browser-support-policy\n'
+      );
+    }
+
     const isProduction = process.env.EMBER_ENV === 'production';
 
     if (

packages/ember/index.js

@@ -170,6 +170,22 @@ import {
 
 const Ember = (typeof context.imports.Ember === 'object' && context.imports.Ember) || {};
 
+const isIE = Boolean(window.MSInputMethodContext) && Boolean(document.documentMode);
+
+deprecate(
+  'Internet Explorer 11 will no longer be supported in the next major version of Ember. For details on the new browser support policy, see the official documentation: http://emberjs.com/browser-support',
+  !isIE,
+  {
+    id: '3-0-browser-support-policy',
+    url: 'https://emberjs.com/deprecations/v3.x#toc_3-0-browser-support-policy',
+    until: '4.0.0',
+    for: 'ember-source',
+    since: {
+      enabled: '3.26.0',
+    },
+  }
+);
+
 Ember.isNamespace = true;
 Ember.toString = function () {
   return 'Ember';

tests/index.html

@@ -66,7 +66,13 @@
           EmberENV.ENABLE_OPTIONAL_FEATURES = true;
         }
 
-        EmberENV['RAISE_ON_DEPRECATION'] = true;
+        var isIE = Boolean(window.MSInputMethodContext) && Boolean(document.documentMode);
+
+        // ignore deprecations for IE11 specifically (due to browser support
+        // policy deprecation, which happens before we can `expectDeprecation`)
+        if (!isIE) {
+          EmberENV['RAISE_ON_DEPRECATION'] = true;
+        }
 
         if (QUnit.urlParams.debugrendertree) {
           EmberENV['_DEBUG_RENDER_TREE'] = true;