Pass error messages from native messaging to web-app.

remoting/webapp/crd/js/native_message_host_log_message_handler.js

+// Copyright 2015 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.
+
+/**
+ * @fileoverview
+ * Class to handle debug log messages sent by either the It2Me or Me2Me native
+ * messaging hosts.
+ */
+
+'use strict';
+
+/** @suppress {duplicate} */
+var remoting = remoting || {};
+
+(function() {
+
+/**
+ * @constructor
+ */
+remoting.NativeMessageHostDebugMessageHandler = function() {
+};
+
+/**
+ * Handle debug messages..
+ *
+ * @param {Object} message
+ * @return {boolean} True if the message was handled.
+ */
+remoting.NativeMessageHostDebugMessageHandler.prototype.handleMessage =
+    function(message)
+{
+  /** @type {string} */
+  var type = base.getStringAttr(message, 'type', '');
+  switch (type) {
+    case '_debug_log':
+      var timestamp = base.timestamp();
+      var msg = base.getStringAttr(message, 'message', '<no message>');
+      var severity = base.getStringAttr(message, 'severity', 'log');
+      var file = base.getStringAttr(message, 'file', '<no file>');
+      var line = base.getNumberAttr(message, 'line', -1);
+      var location = file + ':' + line;
+      var css = 'color: gray; font-style: italic'
+      switch (severity) {
+        case 'error':
+          console.error('%s %s %c%s', timestamp, msg, css, location);
+          break;
+        case 'warn':
+          console.warn('%s %s %c%s', timestamp, msg, css, location);
+          break;
+        default:
+          console.log('%s %s %c%s', timestamp, msg, css, location);
+      };
+      return true;
+  }
+  return false;
+};
+
+})();