Roll chromium to 492629 (#230)

This patch
- rolls chromium to 492629
- migrates connection establishing to use browser target. This migration means
  that now we have a single websocket connection to browser (implemented
  in Connection class). A connection to a particular target is
  incapsulated in a new Session class.

lib/helper.js

@@ -49,7 +49,7 @@ class Helper {
   }
 
   /**
-   * @param {!Connection} client
+   * @param {!Session} client
    * @param {!Object} remoteObject
    * @return {!Promise<!Object>}
    */
@@ -96,7 +96,7 @@ class Helper {
   }
 
   /**
-   * @param {!Connection} client
+   * @param {!Session} client
    * @param {!Object} remoteObject
    * @return {!Promise}
    */