fix(metrics): Ensure emailFirst experiment metrics are reported. (#5402) r=vladikoff

The problem is `createExperiment` was called without a groupType.

fixes #5397

app/scripts/views/mixins/email-first-experiment-mixin.js

@@ -28,13 +28,23 @@ define(function (require, exports, module) {
 
       beforeRender () {
         if (this.isInEmailFirstExperiment()) {
-          this.createExperiment(EXPERIMENT_NAME);
-          if (this.isInEmailFirstExperimentGroup('treatment') && options.treatmentPathname) {
+          const experimentGroup = this.getEmailFirstExperimentGroup();
+          this.createExperiment(EXPERIMENT_NAME, experimentGroup);
+          if (experimentGroup === 'treatment' && options.treatmentPathname) {
             this.replaceCurrentPage(options.treatmentPathname);
           }
         }
       },
 
+      /**
+       * Get the email first experiment group
+       *
+       * @returns {String}
+       */
+      getEmailFirstExperimentGroup () {
+        return this.getExperimentGroup(EXPERIMENT_NAME, this._getEmailFirstExperimentSubject());
+      },
+
       /**
        * Is the user in the email-first experiment?
        *

app/tests/spec/views/mixins/email-first-experiment-mixin.js

@@ -58,9 +58,10 @@ define((require, exports, module) => {
 
     it('exposes the expected interface', () => {
       const mixin = EmailFirstExperimentMixin();
-      assert.lengthOf(Object.keys(mixin), 5);
+      assert.lengthOf(Object.keys(mixin), 6);
       assert.isArray(mixin.dependsOn);
       assert.isFunction(mixin.beforeRender);
+      assert.isFunction(mixin.getEmailFirstExperimentGroup);
       assert.isFunction(mixin.isInEmailFirstExperiment);
       assert.isFunction(mixin.isInEmailFirstExperimentGroup);
       assert.isFunction(mixin._getEmailFirstExperimentSubject);
@@ -122,31 +123,26 @@ define((require, exports, module) => {
 
       it('creates the experiment for users in the control group, does not redirect', () => {
         sandbox.stub(view, 'isInEmailFirstExperiment', () => true);
-        sandbox.stub(view, 'isInEmailFirstExperimentGroup', () => false);
+        sandbox.stub(view, 'getEmailFirstExperimentGroup', () => 'control');
 
         view.beforeRender();
 
         assert.isTrue(view.isInEmailFirstExperiment.calledOnce);
 
-        assert.isTrue(view.isInEmailFirstExperimentGroup.calledOnce);
-        assert.isTrue(view.isInEmailFirstExperimentGroup.calledWith('treatment'));
-
         assert.isTrue(view.createExperiment.calledOnce);
-        assert.isTrue(view.createExperiment.calledWith('emailFirst'));
+        assert.isTrue(view.createExperiment.calledWith('emailFirst', 'control'));
 
         assert.isFalse(view.replaceCurrentPage.called);
       });
 
       it('creates the experiment for users in the treatment group, redirects if treatmentPathname specified', () => {
         sandbox.stub(view, 'isInEmailFirstExperiment', () => true);
-        sandbox.stub(view, 'isInEmailFirstExperimentGroup', () => true);
+        sandbox.stub(view, 'getEmailFirstExperimentGroup', () => 'treatment');
 
         view.beforeRender();
 
-        assert.isTrue(view.isInEmailFirstExperiment.calledOnce);
-
         assert.isTrue(view.createExperiment.calledOnce);
-        assert.isTrue(view.createExperiment.calledWith('emailFirst'));
+        assert.isTrue(view.createExperiment.calledWith('emailFirst', 'treatment'));
 
         assert.isTrue(view.replaceCurrentPage.calledOnce);
         assert.isTrue(view.replaceCurrentPage.calledWith('/'));