Add basic debug log to host page.

remoting/webapp/me2mom/debug_log.js

Index: remoting/webapp/me2mom/debug_log.js
===================================================================
--- remoting/webapp/me2mom/debug_log.js	(revision 0)
+++ remoting/webapp/me2mom/debug_log.js	(revision 0)
@@ -0,0 +1,42 @@
+// Copyright (c) 2011 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.
+
+// Maximum numer of lines to record in the debug log.
+// Only the most recent <n> lines are displayed.
+var MAX_DEBUG_LOG_SIZE = 1000;
+
+function toggleDebugLog() {
+  debugLog = document.getElementById('debug-log');
+  toggleButton = document.getElementById('debug-log-toggle');
+
+  if (!debugLog.style.display || debugLog.style.display == 'none') {
+    debugLog.style.display = 'block';
+    toggleButton.value = 'Hide Debug Log';
+  } else {
+    debugLog.style.display = 'none';
+    toggleButton.value = 'Show Debug Log';
+  }
+}
+
+/**
+ * Add the given message to the debug log.
+ *
+ * @param {string} message The debug info to add to the log.
+ */
+function addToDebugLog(message) {
+  var debugLog = document.getElementById('debug-log');
+
+  // Remove lines from top if we've hit our max log size.
+  if (debugLog.childNodes.length == MAX_DEBUG_LOG_SIZE) {
+    debugLog.removeChild(debugLog.firstChild);
+  }
+
+  // Add the new <p> to the end of the debug log.
+  var p = document.createElement('p');
+  p.appendChild(document.createTextNode(message));
+  debugLog.appendChild(p);
+
+  // Scroll to bottom of div
+  debugLog.scrollTop = debugLog.scrollHeight;
+}