Renames ImageRequest to ImageRequestTask

During a cleanup https://codereview.chromium.org/1148563004 the image
Request class was renamed to ImageRequest. However, the file name was
kept as request.js. Make the class and its file name the same.

Bug: 903742
Change-Id: I6f2d7bbfb6f3f94001d0cd1e629fc27f83061c45
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2245429Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Commit-Queue: Bo Majewski <majewski@chromium.org>
Cr-Commit-Position: refs/heads/master@{#779705}

chrome/browser/chromeos/file_manager/image_loader_jstest.cc

@@ -22,3 +22,7 @@ IN_PROC_BROWSER_TEST_F(ImageLoaderJsTest, CacheTest) {
 IN_PROC_BROWSER_TEST_F(ImageLoaderJsTest, ImageLoaderTest) {
   RunTestURL("image_loader_unittest_gen.html");
 }
+
+IN_PROC_BROWSER_TEST_F(ImageLoaderJsTest, SchedulerTest) {
+  RunTestURL("scheduler_unittest_gen.html");
+}

ui/file_manager/image_loader/BUILD.gn

@@ -14,9 +14,9 @@ js_type_check("closure_compile_module") {
     ":image_loader",
     ":image_loader_client",
     ":image_loader_util",
+    ":image_request_task",
     ":load_image_request",
     ":piex_loader",
-    ":request",
     ":scheduler",
   ]
 }
@@ -39,9 +39,9 @@ js_unittest("cache_unittest") {
 js_library("image_loader") {
   deps = [
     ":cache",
+    ":image_request_task",
     ":load_image_request",
     ":piex_loader",
-    ":request",
     ":scheduler",
     "//ui/file_manager/externs:file_manager_private",
   ]
@@ -96,7 +96,7 @@ js_library("piex_loader") {
   externs_list = [ "//ui/file_manager/externs/platform.js" ]
 }
 
-js_library("request") {
+js_library("image_request_task") {
   deps = [
     ":cache",
     ":image_loader_util",
@@ -108,7 +108,14 @@ js_library("request") {
 }
 
 js_library("scheduler") {
-  deps = [ ":request" ]
+  deps = [ ":image_request_task" ]
+}
+
+js_unittest("scheduler_unittest") {
+  deps = [
+    ":scheduler",
+    "//ui/webui/resources/js:webui_resource_test",
+  ]
 }
 
 js_test_gen_html("js_test_gen_html") {
@@ -117,6 +124,7 @@ js_test_gen_html("js_test_gen_html") {
     ":cache_unittest",
     ":image_loader_client_unittest",
     ":image_loader_unittest",
+    ":scheduler_unittest",
   ]
 }
 

ui/file_manager/image_loader/background_scripts.js

@@ -9,7 +9,7 @@
 // <include src="image_loader.js">
 // <include src="image_loader_util.js">
 // <include src="piex_loader.js">
-// <include src="request.js">
+// <include src="image_request_task.js">
 // <include src="scheduler.js">
 // Entry point.
 // <include src="background.js">

ui/file_manager/image_loader/image_loader.js

@@ -131,7 +131,7 @@ ImageLoader.prototype.onMessage_ = function(senderOrigin, request, callback) {
     return false;  // No callback calls.
   } else {
     // Create a request task and add it to the scheduler (queue).
-    const requestTask = new ImageRequest(
+    const requestTask = new ImageRequestTask(
         requestId, this.cache_, this.piexLoader_, request, callback);
     this.scheduler_.add(requestTask);
     return true;  // Request will call the callback.

ui/file_manager/image_loader/request.js → ui/file_manager/image_loader/image_request_task.js

@@ -13,7 +13,7 @@
  * @param {function(!LoadImageResponse)} callback Response handler.
  * @constructor
  */
-function ImageRequest(id, cache, piexLoader, request, callback) {
+function ImageRequestTask(id, cache, piexLoader, request, callback) {
   /**
    * Global ID (concatenated client ID and client request ID).
    * @type {string}
@@ -111,7 +111,7 @@ function ImageRequest(id, cache, piexLoader, request, callback) {
  * @const
  * @type {number}
  */
-ImageRequest.VIDEO_THUMBNAIL_POSITION = 3; // [sec]
+ImageRequestTask.VIDEO_THUMBNAIL_POSITION = 3;  // [sec]
 
 /**
  * The maximum milliseconds to load video. If loading video exceeds the limit,
@@ -119,13 +119,13 @@ ImageRequest.VIDEO_THUMBNAIL_POSITION = 3; // [sec]
  * @const
  * @type {number}
  */
-ImageRequest.MAX_MILLISECONDS_TO_LOAD_VIDEO = 3000;
+ImageRequestTask.MAX_MILLISECONDS_TO_LOAD_VIDEO = 3000;
 
 /**
  * A map which is used to estimate content type from extension.
  * @enum {string}
  */
-ImageRequest.ExtensionContentTypeMap = {
+ImageRequestTask.ExtensionContentTypeMap = {
   gif: 'image/gif',
   png: 'image/png',
   svg: 'image/svg',
@@ -138,7 +138,7 @@ ImageRequest.ExtensionContentTypeMap = {
  * Returns ID of the request.
  * @return {string} Request ID.
  */
-ImageRequest.prototype.getId = function() {
+ImageRequestTask.prototype.getId = function() {
   return this.id_;
 };
 
@@ -146,7 +146,7 @@ ImageRequest.prototype.getId = function() {
  * Returns the client's task ID for the request.
  * @return {number}
  */
-ImageRequest.prototype.getClientTaskId = function() {
+ImageRequestTask.prototype.getClientTaskId = function() {
   // Every incoming request should have been given a taskId.
   assert(this.request_.taskId);
   return this.request_.taskId;
@@ -158,7 +158,7 @@ ImageRequest.prototype.getClientTaskId = function() {
  *
  * @return {number} Priority.
  */
-ImageRequest.prototype.getPriority = function() {
+ImageRequestTask.prototype.getPriority = function() {
   return (this.request_.priority !== undefined) ? this.request_.priority : 2;
 };
 
@@ -169,7 +169,7 @@ ImageRequest.prototype.getPriority = function() {
  * @param {function()} onSuccess Success callback.
  * @param {function()} onFailure Failure callback.
  */
-ImageRequest.prototype.loadFromCacheAndProcess = function(
+ImageRequestTask.prototype.loadFromCacheAndProcess = function(
     onSuccess, onFailure) {
   this.loadFromCache_(
       function(width, height, ifd, data) {  // Found in cache.
@@ -185,14 +185,14 @@ ImageRequest.prototype.loadFromCacheAndProcess = function(
  *
  * @param {function()} callback Completion callback.
  */
-ImageRequest.prototype.downloadAndProcess = function(callback) {
+ImageRequestTask.prototype.downloadAndProcess = function(callback) {
   if (this.downloadCallback_) {
     throw new Error('Downloading already started.');
   }
 
   this.downloadCallback_ = callback;
-  this.downloadOriginal_(this.onImageLoad_.bind(this),
-                         this.onImageError_.bind(this));
+  this.downloadOriginal_(
+      this.onImageLoad_.bind(this), this.onImageError_.bind(this));
 };
 
 /**
@@ -203,7 +203,7 @@ ImageRequest.prototype.downloadAndProcess = function(callback) {
  * @param {function()} onFailure Failure callback.
  * @private
  */
-ImageRequest.prototype.loadFromCache_ = function(onSuccess, onFailure) {
+ImageRequestTask.prototype.loadFromCache_ = function(onSuccess, onFailure) {
   const cacheKey = LoadImageRequest.cacheKey(this.request_);
 
   if (!cacheKey) {
@@ -238,7 +238,7 @@ ImageRequest.prototype.loadFromCache_ = function(onSuccess, onFailure) {
  * @param {string} data Image data.
  * @private
  */
-ImageRequest.prototype.saveToCache_ = function(width, height, data) {
+ImageRequestTask.prototype.saveToCache_ = function(width, height, data) {
   const timestamp = this.request_.timestamp;
 
   if (!this.request_.cache || !timestamp) {
@@ -262,7 +262,7 @@ ImageRequest.prototype.saveToCache_ = function(width, height, data) {
  * @param {function()} onFailure Failure callback.
  * @private
  */
-ImageRequest.prototype.downloadOriginal_ = function(onSuccess, onFailure) {
+ImageRequestTask.prototype.downloadOriginal_ = function(onSuccess, onFailure) {
   this.image_.onload = function() {
     URL.revokeObjectURL(this.image_.src);
     onSuccess();
@@ -324,9 +324,11 @@ ImageRequest.prototype.downloadOriginal_ = function(onSuccess, onFailure) {
 
   // Load video thumbnails by using video tag instead of XHR.
   if (fileType.type === 'video') {
-    this.createVideoThumbnailUrl_(this.request_.url).then(function(url) {
+    this.createVideoThumbnailUrl_(this.request_.url)
+        .then(function(url) {
           this.image_.src = url;
-    }.bind(this)).catch(function(error) {
+        }.bind(this))
+        .catch(function(error) {
           console.error('Video thumbnail error: ', error);
           onFailure();
         });
@@ -353,7 +355,7 @@ ImageRequest.prototype.downloadOriginal_ = function(onSuccess, onFailure) {
  *    thumbnail.
  * @private
  */
-ImageRequest.prototype.createVideoThumbnailUrl_ = function(url) {
+ImageRequestTask.prototype.createVideoThumbnailUrl_ = function(url) {
   const video =
       assertInstanceof(document.createElement('video'), HTMLVideoElement);
   return Promise
@@ -361,13 +363,13 @@ ImageRequest.prototype.createVideoThumbnailUrl_ = function(url) {
         new Promise((resolve, reject) => {
           video.addEventListener('canplay', resolve);
           video.addEventListener('error', reject);
-          video.currentTime = ImageRequest.VIDEO_THUMBNAIL_POSITION;
+          video.currentTime = ImageRequestTask.VIDEO_THUMBNAIL_POSITION;
           video.preload = 'auto';
           video.src = url;
           video.load();
         }),
         new Promise((resolve) => {
-          setTimeout(resolve, ImageRequest.MAX_MILLISECONDS_TO_LOAD_VIDEO);
+          setTimeout(resolve, ImageRequestTask.MAX_MILLISECONDS_TO_LOAD_VIDEO);
         }).then(() => {
           // If we don't receive 'canplay' event after 3 seconds have passed for
           // some reason (e.g. unseekable video), we give up generating
@@ -396,7 +398,7 @@ ImageRequest.prototype.createVideoThumbnailUrl_ = function(url) {
  *     type and the fetched data.
  * @param {function()} onFailure Failure callback.
  */
-ImageRequest.prototype.load = function(url, onSuccess, onFailure) {
+ImageRequestTask.prototype.load = function(url, onSuccess, onFailure) {
   this.aborted_ = false;
 
   // Do not call any callbacks when aborting.
@@ -405,7 +407,8 @@ ImageRequest.prototype.load = function(url, onSuccess, onFailure) {
         // When content type is not available, try to estimate it from url.
         if (!contentType) {
           contentType =
-              ImageRequest.ExtensionContentTypeMap[this.extractExtension_(url)];
+              ImageRequestTask
+                  .ExtensionContentTypeMap[this.extractExtension_(url)];
         }
 
         if (!this.aborted_) {
@@ -422,7 +425,8 @@ ImageRequest.prototype.load = function(url, onSuccess, onFailure) {
   // The query parameter is workaround for crbug.com/379678, which forces the
   // browser to obtain the latest contents of the image.
   const noCacheUrl = url + '?nocache=' + Date.now();
-  this.xhr_ = ImageRequest.load_(noCacheUrl, onMaybeSuccess, onMaybeFailure);
+  this.xhr_ =
+      ImageRequestTask.load_(noCacheUrl, onMaybeSuccess, onMaybeFailure);
 };
 
 /**
@@ -430,7 +434,7 @@ ImageRequest.prototype.load = function(url, onSuccess, onFailure) {
  * @param {string} url Url.
  * @return {string} Extracted extension, e.g. png.
  */
-ImageRequest.prototype.extractExtension_ = function(url) {
+ImageRequestTask.prototype.extractExtension_ = function(url) {
   const result = (/\.([a-zA-Z]+)$/i).exec(url);
   return result ? result[1] : '';
 };
@@ -446,7 +450,7 @@ ImageRequest.prototype.extractExtension_ = function(url) {
  * @return {XMLHttpRequest} XHR instance.
  * @private
  */
-ImageRequest.load_ = function(url, onSuccess, onFailure) {
+ImageRequestTask.load_ = function(url, onSuccess, onFailure) {
   const xhr = new XMLHttpRequest();
   xhr.responseType = 'blob';
 
@@ -481,7 +485,7 @@ ImageRequest.load_ = function(url, onSuccess, onFailure) {
  * @param {boolean} imageChanged Whether the image has been changed.
  * @private
  */
-ImageRequest.prototype.sendImage_ = function(imageChanged) {
+ImageRequestTask.prototype.sendImage_ = function(imageChanged) {
   let width;
   let height;
   let data;
@@ -525,7 +529,7 @@ ImageRequest.prototype.sendImage_ = function(imageChanged) {
  * @param {string} data Image data.
  * @private
  */
-ImageRequest.prototype.sendImageData_ = function(width, height, data) {
+ImageRequestTask.prototype.sendImageData_ = function(width, height, data) {
   const result = {width, height, ifd: this.ifd_, data};
   this.sendResponse_(new LoadImageResponse(
       LoadImageResponseStatus.SUCCESS, this.getClientTaskId(), result));
@@ -536,7 +540,7 @@ ImageRequest.prototype.sendImageData_ = function(width, height, data) {
  * and finalizes the request process.
  * @private
  */
-ImageRequest.prototype.onImageLoad_ = function() {
+ImageRequestTask.prototype.onImageLoad_ = function() {
   // Perform processing if the url is not a data url, or if there are some
   // operations requested.
   if (!(this.request_.url.match(/^data/) ||
@@ -559,7 +563,7 @@ ImageRequest.prototype.onImageLoad_ = function() {
  * finalizes the request process.
  * @private
  */
-ImageRequest.prototype.onImageError_ = function() {
+ImageRequestTask.prototype.onImageError_ = function() {
   this.sendResponse_(new LoadImageResponse(
       LoadImageResponseStatus.ERROR, this.getClientTaskId()));
   this.cleanup_();
@@ -569,7 +573,7 @@ ImageRequest.prototype.onImageError_ = function() {
 /**
  * Cancels the request.
  */
-ImageRequest.prototype.cancel = function() {
+ImageRequestTask.prototype.cancel = function() {
   this.cleanup_();
 
   // If downloading has started, then call the callback.
@@ -582,7 +586,7 @@ ImageRequest.prototype.cancel = function() {
  * Cleans up memory used by this request.
  * @private
  */
-ImageRequest.prototype.cleanup_ = function() {
+ImageRequestTask.prototype.cleanup_ = function() {
   this.image_.onerror = function() {};
   this.image_.onload = function() {};
 

ui/file_manager/image_loader/scheduler.js

@@ -3,43 +3,44 @@
 // found in the LICENSE file.
 
 /**
- * Scheduler for requests. Fetches requests from a queue and processes them
- * synchronously, taking into account priorities. The highest priority is 0.
+ * Scheduler for ImageRequestTask objects. Fetches tasks from a queue and
+ * processes them synchronously, taking into account priorities. The highest
+ * priority is 0.
  * @constructor
  */
 function Scheduler() {
   /**
-   * List of requests waiting to be checked. If these items are available in
+   * List of tasks waiting to be checked. If these items are available in
    * cache, then they are processed immediately after starting the scheduler.
-   * However, if they have to be downloaded, then these requests are moved
-   * to pendingRequests_.
+   * However, if they have to be downloaded, then these tasks are moved
+   * to pendingTasks_.
    *
-   * @type {Array<ImageRequest>}
+   * @type {Array<ImageRequestTask>}
    * @private
    */
-  this.newRequests_ = [];
+  this.newTasks_ = [];
 
   /**
-   * List of pending requests for images to be downloaded.
-   * @type {Array<ImageRequest>}
+   * List of pending tasks for images to be downloaded.
+   * @type {Array<ImageRequestTask>}
    * @private
    */
-  this.pendingRequests_ = [];
+  this.pendingTasks_ = [];
 
   /**
-   * List of requests being processed.
-   * @type {Array<ImageRequest>}
+   * List of tasks being processed.
+   * @type {Array<ImageRequestTask>}
    * @private
    */
-  this.activeRequests_ = [];
+  this.activeTasks_ = [];
 
   /**
-   * Map of requests being added to the queue, but not finalized yet. Keyed by
-   * the ImageRequest id.
-   * @type {Object<string, ImageRequest>}>
+   * Map of tasks being added to the queue, but not finalized yet. Keyed by
+   * the ImageRequestTask id.
+   * @type {Object<string, ImageRequestTask>}>
    * @private
    */
-  this.requests_ = {};
+  this.tasks_ = {};
 
   /**
    * If the scheduler has been started.
@@ -50,121 +51,119 @@ function Scheduler() {
 }
 
 /**
- * Maximum download requests to be run in parallel.
+ * Maximum download tasks to be run in parallel.
  * @type {number}
  * @const
  */
 Scheduler.MAXIMUM_IN_PARALLEL = 5;
 
 /**
- * Adds a request to the internal priority queue and executes it when requests
+ * Adds a task to the internal priority queue and executes it when tasks
  * with higher priorities are finished. If the result is cached, then it is
  * processed immediately once the scheduler is started.
  *
- * @param {ImageRequest} request Request object.
+ * @param {ImageRequestTask} task A task to be run
  */
-Scheduler.prototype.add = function(request) {
+Scheduler.prototype.add = function(task) {
   if (!this.started_) {
-    this.newRequests_.push(request);
-    this.requests_[request.getId()] = request;
+    this.newTasks_.push(task);
+    this.tasks_[task.getId()] = task;
     return;
   }
 
-  // Enqueue the request, since already started.
-  this.pendingRequests_.push(request);
-  this.sortPendingRequests_();
+  // Enqueue the tasks, since already started.
+  this.pendingTasks_.push(task);
+  this.sortPendingTasks_();
 
   this.continue_();
 };
 
 /**
- * Removes a request from the scheduler (if exists).
- * @param {string} requestId Unique ID of the request.
+ * Removes a task from the scheduler (if exists).
+ * @param {string} taskId Unique ID of the task.
  */
-Scheduler.prototype.remove = function(requestId) {
-  const request = this.requests_[requestId];
-  if (!request) {
+Scheduler.prototype.remove = function(taskId) {
+  const task = this.tasks_[taskId];
+  if (!task) {
     return;
   }
 
   // Remove from the internal queues with pending tasks.
-  const newIndex = this.pendingRequests_.indexOf(request);
+  const newIndex = this.newTasks_.indexOf(task);
   if (newIndex != -1) {
-    this.newRequests_.splice(newIndex, 1);
+    this.newTasks_.splice(newIndex, 1);
   }
-  const pendingIndex = this.pendingRequests_.indexOf(request);
+  const pendingIndex = this.pendingTasks_.indexOf(task);
   if (pendingIndex != -1) {
-    this.pendingRequests_.splice(pendingIndex, 1);
+    this.pendingTasks_.splice(pendingIndex, 1);
   }
 
-  // Cancel the request.
-  request.cancel();
-  delete this.requests_[requestId];
+  // Cancel the task.
+  task.cancel();
+  delete this.tasks_[taskId];
 };
 
 /**
- * Starts handling requests.
+ * Starts handling tasks.
  */
 Scheduler.prototype.start = function() {
   this.started_ = true;
 
   // Process tasks added before scheduler has been started.
-  this.pendingRequests_ = this.newRequests_;
-  this.sortPendingRequests_();
-  this.newRequests_ = [];
+  this.pendingTasks_ = this.newTasks_;
+  this.sortPendingTasks_();
+  this.newTasks_ = [];
 
-  // Start serving enqueued requests.
+  // Start serving enqueued tasks.
   this.continue_();
 };
 
 /**
- * Sorts pending requests by priorities.
+ * Sorts pending tasks by priorities.
  * @private
  */
-Scheduler.prototype.sortPendingRequests_ = function() {
-  this.pendingRequests_.sort(function(a, b) {
+Scheduler.prototype.sortPendingTasks_ = function() {
+  this.pendingTasks_.sort(function(a, b) {
     return a.getPriority() - b.getPriority();
   });
 };
 
 /**
- * Processes pending requests from the queue. There is no guarantee that
+ * Processes pending tasks from the queue. There is no guarantee that
  * all of the tasks will be processed at once.
  *
  * @private
  */
 Scheduler.prototype.continue_ = function() {
   // Run only up to MAXIMUM_IN_PARALLEL in the same time.
-  while (this.pendingRequests_.length &&
-         this.activeRequests_.length < Scheduler.MAXIMUM_IN_PARALLEL) {
-    const request = this.pendingRequests_.shift();
-    this.activeRequests_.push(request);
+  while (this.pendingTasks_.length &&
+         this.activeTasks_.length < Scheduler.MAXIMUM_IN_PARALLEL) {
+    const task = this.pendingTasks_.shift();
+    this.activeTasks_.push(task);
 
     // Try to load from cache. If doesn't exist, then download.
-    request.loadFromCacheAndProcess(
-        this.finish_.bind(this, request),
-        function(currentRequest) {
-          currentRequest.downloadAndProcess(
-              this.finish_.bind(this, currentRequest));
-        }.bind(this, request));
+    task.loadFromCacheAndProcess(
+        this.finish_.bind(this, task), function(currentTask) {
+          currentTask.downloadAndProcess(this.finish_.bind(this, currentTask));
+        }.bind(this, task));
   }
 };
 
 /**
- * Handles finished requests.
+ * Handles finished tasks.
  *
- * @param {ImageRequest} request Finished request.
+ * @param {ImageRequestTask} task Finished task.
  * @private
  */
-Scheduler.prototype.finish_ = function(request) {
-  const index = this.activeRequests_.indexOf(request);
+Scheduler.prototype.finish_ = function(task) {
+  const index = this.activeTasks_.indexOf(task);
   if (index < 0) {
-    console.warn('Request not found.');
+    console.warn('ImageRequestTask not found.');
   }
-  this.activeRequests_.splice(index, 1);
-  delete this.requests_[request.getId()];
+  this.activeTasks_.splice(index, 1);
+  delete this.tasks_[task.getId()];
 
-  // Continue handling the most important requests (if started).
+  // Continue handling the most important tasks (if started).
   if (this.started_) {
     this.continue_();
   }

ui/file_manager/image_loader/scheduler_unittest.js

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+'use strict';
+
+/**
+ * Fake global clock used to record the "time" at which a task was run.
+ */
+let globalTime = 0;
+
+function setUp() {
+  globalTime = 0;
+}
+
+/**
+ * @typedef{{
+ *   cancelCallCount: number,
+ *   runTime: number,
+ * }}
+ */
+let FakeImageRequestTask;
+
+/**
+ * @param {string} taskId
+ * @return {!FakeImageRequestTask}
+ */
+function newTask(taskId, priority) {
+  return /** @type !FakeImageRequestTask */ ({
+    // Counts how many times cancel method was called.
+    // Used to test multiple cancellation of the same task.
+    cancelCallCount: 0,
+
+    // Records value of globalTime variable at the time the main method,
+    // loadFromCacheAndProcess is called. Used to test if the task was
+    // executed and in what orders tasks were executed.
+    runTime: 0,
+
+    getId() {
+      return taskId;
+    },
+    getPriority() {
+      return priority;
+    },
+    cancel() {
+      ++this.cancelCallCount;
+    },
+    loadFromCacheAndProcess(resolve, reject) {
+      this.runTime = ++globalTime;
+      setTimeout(resolve);
+    },
+  });
+}
+
+/**
+ * Checks that adding and removing tasks before the scheduler is started works.
+ */
+function testIdleSchedulerAddRemove() {
+  const scheduler = new Scheduler();
+  const fakeTask = newTask('task-1', 0);
+  scheduler.add(/** @type {!ImageRequestTask} */ (fakeTask));
+  assertEquals(0, fakeTask.cancelCallCount);
+  scheduler.remove('task-1');
+  assertEquals(1, fakeTask.cancelCallCount);
+  scheduler.remove('task-1');
+  assertEquals(1, fakeTask.cancelCallCount);
+}
+
+/**
+ * Checks that tasks that were in newTasks are correctly copied to pending
+ * tasks when scheduler is started. They also should be executed in the
+ * order of their priorities.
+ */
+function testNewTasksMovedAndRunInPriorityOrder() {
+  const fakeTask1 = newTask('task-1', 1);
+  const fakeTask2 = newTask('task-2', 0);
+
+  const scheduler = new Scheduler();
+  scheduler.add(/** @type {!ImageRequestTask} */ (fakeTask1));
+  scheduler.add(/** @type {!ImageRequestTask} */ (fakeTask2));
+
+  scheduler.start();
+  assertEquals(2, fakeTask1.runTime);
+  assertEquals(1, fakeTask2.runTime);
+}
+
+/**
+ * Checks that the scheduler only launches MAXIMUM_IN_PARALLEL tasks.
+ */
+function testParallelTasks() {
+  const scheduler = new Scheduler();
+  const taskList = [];
+  for (let i = 0; i <= Scheduler.MAXIMUM_IN_PARALLEL; ++i) {
+    taskList.push(newTask(`task-${i}`, 0));
+    scheduler.add(/** @type {!ImageRequestTask} */ (taskList[i]));
+  }
+  scheduler.start();
+  for (let i = 0; i < Scheduler.MAXIMUM_IN_PARALLEL; ++i) {
+    assertEquals(i + 1, taskList[i].runTime, `task ${i} did not run`);
+  }
+  assertEquals(0, taskList[Scheduler.MAXIMUM_IN_PARALLEL].runTime);
+}