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

ui/file_manager/integration_tests/remote_call.js

Index: ui/file_manager/integration_tests/remote_call.js
diff --git a/ui/file_manager/integration_tests/remote_call.js b/ui/file_manager/integration_tests/remote_call.js
index 54c59e311712789ca6484962238fb9bd0e82cfe4..f9815b03da8cba47bef3a51d1160cd1557a47c74 100644
--- a/ui/file_manager/integration_tests/remote_call.js
+++ b/ui/file_manager/integration_tests/remote_call.js
@@ -15,6 +15,16 @@ function RemoteCall(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.
@@ -27,19 +37,40 @@ 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]);
-        });
+  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));
 };