diff -r 000000000000 -r 6474c204b198 testing/marionette/marionette-common.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/testing/marionette/marionette-common.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,96 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ *
+ * This file contains common code that is shared between marionette-server.js
+ * and marionette-listener.js.
+ *
+ */
+
+/**
+ * Creates an error message for a JavaScript exception thrown during
+ * execute_(async_)script.
+ *
+ * This will generate a [msg, trace] pair like:
+ *
+ * ['ReferenceError: foo is not defined',
+ *  'execute_script @test_foo.py, line 10
+ *   inline javascript, line 2
+ *   src: "return foo;"']
+ *
+ * @param error An Error object passed to a catch() clause.
+          fnName The name of the function to use in the stack trace message
+                 (e.g., 'execute_script').
+          pythonFile The filename of the test file containing the Marionette
+                  command that caused this exception to occur.
+          pythonLine The line number of the above test file.
+          script The JS script being executed in text form.
+ */
+this.createStackMessage = function createStackMessage(error, fnName, pythonFile,
+  pythonLine, script) {
+  let python_stack = fnName + " @" + pythonFile;
+  if (pythonLine !== null) {
+    python_stack += ", line " + pythonLine;
+  }
+  let trace, msg;
+  if (typeof(error) == "object" && 'name' in error && 'stack' in error) {
+    let stack = error.stack.split("\n");
+    let match = stack[0].match(/:(\d+):\d+$/);
+    let line = match ? parseInt(match[1]) : 0;
+    msg = error.name + ('message' in error ? ": " + error.message : "");
+    trace = python_stack +
+                "\ninline javascript, line " + line +
+                "\nsrc: \"" + script.split("\n")[line] + "\"";
+  }
+  else {
+    trace = python_stack;
+    msg = error + "";
+  }
+  return [msg, trace];
+}
+
+this.MarionetteLogObj = function MarionetteLogObj() {
+  this.logs = [];
+}
+MarionetteLogObj.prototype = {
+  /**
+   * Log message. Accepts user defined log-level.
+   * @param msg String
+   *        The message to be logged
+   * @param level String
+   *        The logging level to be used
+   */
+  log: function ML_log(msg, level) {
+    let lev = level ? level : "INFO";
+    this.logs.push( [lev, msg, (new Date()).toString()]);
+  },
+
+  /**
+   * Add a list of logs to its list
+   * @param msgs Object
+   *        Takes a list of strings
+   */
+  addLogs: function ML_addLogs(msgs) {
+    for (let i = 0; i < msgs.length; i++) {
+      this.logs.push(msgs[i]);
+    }
+  },
+  
+  /**
+   * Return all logged messages.
+   */
+  getLogs: function ML_getLogs() {
+    let logs = this.logs;
+    this.clearLogs();
+    return logs;
+  },
+
+  /**
+   * Clears the logs
+   */
+  clearLogs: function ML_clearLogs() {
+    this.logs = [];
+  },
+}