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

To debug tests, they need to be executed with the following switches:
--remote-debugging-port=9222
--enable-file-manager-step-by-step-tests
--enable-pixel-output-in-tests
--ui-test-action-timeout=10000000

Then run http://localhost:9222 in a separate browser window, then select
"chrome manager browser tests" and follow instructions.

TEST=Tested manually.
BUG=460813

Review URL: https://codereview.chromium.org/942393002

Cr-Commit-Position: refs/heads/master@{#317559}

ui/file_manager/integration_tests/file_manager_test_manifest.json

@@ -36,6 +36,7 @@
   "permissions": [
     "fileSystem",
     "tabs",
+    "commandLinePrivate",
     "chrome-extension://oobinhbdbiehknkpbpejbbpdbkdjmoco/*",
     "chrome-extension://hhaomjibdihmijegdhdafkllkbggdgoj/*"
   ]

ui/file_manager/integration_tests/gallery_test_manifest.json

@@ -6,5 +6,6 @@
   "manifest_version": 2,
   "web_accessible_resources": ["*"],
   "background": {"scripts": ["gallery/background.js"]},
-  "incognito" : "split"
+  "incognito" : "split",
+  "permissions": ["commandLinePrivate"]
 }

ui/file_manager/integration_tests/remote_call.js

@@ -14,6 +14,17 @@ 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-file-manager-step-by-step-tests', fulfill);
+  });
+};
+
 /**
  * Calls a remote test util in Files.app's extension. See: test_util.js.
  *
@@ -27,19 +38,37 @@ function RemoteCall(extensionId) {
  */
 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]);
-        });
+  return RemoteCall.isStepByStepEnabled().then(function(stepByStep) {
+    if (!stepByStep)
+      return false;
+    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(stepByStep);
+      };
+    });
+  }).then(function(stepByStep) {
+    return new Promise(function(onFulfilled) {
+      chrome.runtime.sendMessage(
+          this.extensionId_,
+          {
+            func: func,
+            appId: appId,
+            args: args
+          },
+          function(var_args) {
+            if (stepByStep) {
+              console.info('Returned value:');
+              console.info(arguments);
+            }
+            if (opt_callback)
+              opt_callback.apply(null, arguments);
+            onFulfilled(arguments[0]);
+          });
+    }.bind(this));
   }.bind(this));
 };
 

ui/file_manager/integration_tests/video_player_test_manifest.json

@@ -12,5 +12,6 @@
       "video_player/background.js",
       "video_player/open_video_files.js"
     ]},
-  "incognito" : "split"
+  "incognito" : "split",
+  "permissions": ["commandLinePrivate"]
 }