Give access to angular $injector via chrome (#15267)

* Implement getActiveInjector

* Fix typo in comments

* Rename method to sound more frightening

* Move test utils

* Add more documentation

* Fix typo in comment

* Fix name of method in comments

src/test_utils/public/stub_get_active_injector.js

@@ -0,0 +1,44 @@
+/**
+ * This test file contains stubs for chrome.dangerouslyGetActiveInjector, that you will
+ * need to load if any part of the code you are testing relies on that method.
+ * You will need to call setupInjectorStub and teardownInjectorStub in specific
+ * places inside your test file to setup and teardown the stub.
+ * If you can call both of them at the same place you can also use the shortcut
+ * setupAndTeardownInjectorStub instead.
+ */
+
+import ngMock from 'ng_mock';
+
+import chrome from 'ui/chrome';
+import sinon from 'sinon';
+
+/**
+ * This method setups the stub for chrome.dangerouslyGetActiveInjector. You must call it in
+ * a place where beforeEach is allowed to be called (read: inside your describe)
+ * method. You must call this AFTER you've called `ngMock.module` to setup the modules,
+ * but BEFORE you first execute code, that uses chrome.getActiveInjector.
+ */
+export function setupInjectorStub() {
+  beforeEach(ngMock.inject(($injector) => {
+    sinon.stub(chrome, 'dangerouslyGetActiveInjector').returns(Promise.resolve($injector));
+  }));
+}
+
+/**
+ * This methods tears down the stub for chrome.dangerouslyGetActiveInjector. You must call it
+ * in a place where afterEach is allowed to be called.
+ */
+export function teardownInjectorStub() {
+  afterEach(() => {
+    chrome.getActiveInjector.restore();
+  });
+}
+
+/**
+ * This method combines setupInjectorStub and teardownInjectorStub in one method.
+ * It can be used if you can call the other two methods directly behind each other.
+ */
+export function setupAndTeardownInjectorStub() {
+  setupInjectorStub();
+  teardownInjectorStub();
+}

src/ui/public/chrome/chrome.js

@@ -46,7 +46,34 @@ templateApi(chrome, internals);
 themeApi(chrome, internals);
 translationsApi(chrome, internals);
 
-chrome.bootstrap = function () {
-  chrome.setupAngular();
-  angular.bootstrap(document.body, ['kibana']);
+const waitForBootstrap = new Promise(resolve => {
+  chrome.bootstrap = function () {
+    chrome.setupAngular();
+    angular.bootstrap(document.body, ['kibana']);
+    resolve();
+  };
+});
+
+/**
+ * ---- ATTENTION: Read documentation carefully before using this! ----
+ *
+ * Returns a promise, that resolves with an instance of the currently used Angular
+ * $injector service for usage outside of Angular.
+ * You can use this injector to get access to any other injectable component (service,
+ * constant, etc.) by using its get method.
+ *
+ * If you ever use Angular outside of an Angular context via this method, you should
+ * be really sure you know what you are doing!
+ *
+ * When using this method inside your code, you will need to stub it while running
+ * tests. Look into 'src/test_utils/public/stub_get_active_injector' for more information.
+ */
+chrome.dangerouslyGetActiveInjector = () => {
+  return waitForBootstrap.then(() => {
+    const $injector = angular.element(document.body).injector();
+    if (!$injector) {
+      return Promise.reject('document.body had no angular context after bootstrapping');
+    }
+    return $injector;
+  });
 };