[web] add includeReferer flag to SplitTestHandler.getAssignment (#33235)

* [web] add includeReferer flag to SplitTestHandler.getAssignment

* [web] tests: migrate User.getSplitTestAssignment to async/await

I don't want to fight with callbacks and optional arguments. Just move
it to async/await. New tests should use async/await, so there is no
point in making this work in callback-hell.

* [web] remove unused URL import

GitOrigin-RevId: 6251001e6ba7354f704fa663be8ef365ca0b9d23

services/web/test/acceptance/src/helpers/InitApp.mjs

@@ -53,10 +53,11 @@ before('start main app', function (done) {
     route => route.path && route.path === '/dev/csrf',
     router => {
       router.get('/dev/split_test/get_assignment', (req, res) => {
-        const { splitTestName } = req.query
+        const { splitTestName, includeReferer } = req.query
         SplitTestHandler.promises
           .getAssignment(req, res, splitTestName, {
             sync: true,
+            includeReferer: includeReferer === 'true',
           })
           .then(assignment => res.json(assignment))
           .catch(error => {

services/web/test/acceptance/src/helpers/User.mjs

@@ -100,37 +100,6 @@ class User {
     })
   }
 
-  getSplitTestAssignment(splitTestName, query, callback) {
-    if (!callback) {
-      callback = query
-    }
-    const params = new URLSearchParams({
-      splitTestName,
-      ...query,
-    }).toString()
-    this.request.get(
-      {
-        url: `/dev/split_test/get_assignment?${params}`,
-      },
-      (err, response, body) => {
-        if (err != null) {
-          return callback(err)
-        }
-        if (response.statusCode !== 200) {
-          return callback(
-            new Error(
-              `get split test assignment failed: status=${
-                response.statusCode
-              } body=${JSON.stringify(body)}`
-            )
-          )
-        }
-        const assignment = JSON.parse(response.body)
-        callback(null, assignment)
-      }
-    )
-  }
-
   doSessionMaintenance(callback) {
     this.request.post(
       {
@@ -1350,4 +1319,29 @@ User.promises.prototype.doRequest = async function (method, params) {
   })
 }
 
+User.promises.prototype.getSplitTestAssignment = async function (
+  splitTestName,
+  query,
+  referer,
+  includeReferer
+) {
+  const params = new URLSearchParams({
+    splitTestName,
+    includeReferer,
+    ...query,
+  }).toString()
+  const { response, body } = await this.doRequest('GET', {
+    url: `/dev/split_test/get_assignment?${params}`,
+    headers: { referer },
+  })
+  if (response.statusCode !== 200) {
+    throw new Error(
+      `get split test assignment failed: status=${
+        response.statusCode
+      } body=${JSON.stringify(body)}`
+    )
+  }
+  return JSON.parse(response.body)
+}
+
 export default User