Add a simple way of performing step by step tests for testers.

ui/file_manager/integration_tests/remote_call.js

 // Copyright 2014 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';
 
 /**
  * Class to manipulate the window in the remote extension.
  *
  * @param {string} extensionId ID of extension to be manipulated.
  * @constructor
  */
 function RemoteCall(extensionId) {
   this.extensionId_ = extensionId;
 }
 
 /**
+ * Checks whether step by step tests are enabled or not.
+ * @return {Promise<bool>}
+ */
+RemoteCall.isStepByStepEnabled = function() {
+  return new Promise(function(fulfill) {
+    chrome.commandLinePrivate.hasSwitch('enable-step-by-step-tests', fulfill);
+  });
+};
+
+/**
  * Calls a remote test util in Files.app's extension. See: test_util.js.
  *
  * @param {string} func Function name.
  * @param {?string} appId Target window's App ID or null for functions
  *     not requiring a window.
  * @param {Array.<*>} args Array of arguments.
  * @param {function(*)=} opt_callback Callback handling the function's result.
  * @return {Promise} Promise to be fulfilled with the result of the remote
  *     utility.
  */
 RemoteCall.prototype.callRemoteTestUtil =
     function(func, appId, args, opt_callback) {
-  return new Promise(function(onFulfilled) {
-    chrome.runtime.sendMessage(
-        this.extensionId_,
-        {
-          func: func,
-          appId: appId,
-          args: args
-        },
-        function() {
-          if (opt_callback)
-            opt_callback.apply(null, arguments);
-          onFulfilled(arguments[0]);
-        });
+  var stepByStepEnabled = false;
+  return RemoteCall.isStepByStepEnabled().then(function(enabled) {
+    stepByStepEnabled = enabled;
+  }).then(function() {

[hirono, 2015/02/23 07:00:40]

nit: We can receive stepByStepEnabled directly from isStepByStepEnabled, and can
return new Promise of #56 in this function so that #65 can refer
isStepByStepEnabled in this scope.

[mtomasz, 2015/02/23 09:30:43]

I'm not sure if I understand. You mean to embed #56-#73 in a function passed to
isStepByStepEnabled().then()? That would increase indentations. How about now,
just passing "enabled" via promises to the second element of the chain? WDYT?

[hirono, 2015/02/23 10:01:10]

SGTM!

+    if (stepByStepEnabled) {
+      return new Promise(function(onFulfilled) {
+        console.info('Executing: ' + func + ' on ' + appId + ' with args: ');
+        console.info(args);
+        console.info('Type step() to continue...');
+        window.step = function() {
+          window.step = null;
+          onFulfilled();
+        };
+      });
+    }
+  }).then(function() {
+    return new Promise(function(onFulfilled) {
+      chrome.runtime.sendMessage(
+          this.extensionId_,
+          {
+            func: func,
+            appId: appId,
+            args: args
+          },
+          function(var_args) {
+            if (stepByStepEnabled) {
+              console.info('Returned value:');
+              console.info(arguments);
+            }
+            if (opt_callback)
+              opt_callback.apply(null, arguments);
+            onFulfilled(arguments[0]);
+          });
+    }.bind(this));
   }.bind(this));
 };
 
 /**
  * Waits until a window having the given ID prefix appears.
  * @param {string} windowIdPrefix ID prefix of the requested window.
  * @return {Promise} promise Promise to be fulfilled with a found window's ID.
  */
 RemoteCall.prototype.waitForWindow = function(windowIdPrefix) {
   return repeatUntil(function() {
@@ skipping 246 matching lines @@
 RemoteCallFilesApp.prototype.waitUntilCurrentDirectoryIsChanged =
     function(windowId, expectedPath) {
   return repeatUntil(function () {
     return this.callRemoteTestUtil('getBreadcrumbPath', windowId, []).then(
       function(path) {
         if(path !== expectedPath)
           return pending('Expected path is %s', expectedPath);
       });
   }.bind(this));
 };