Roll chromium to r496140 (#465)

This patch rolls chromium to r496140. This includes the r496130 that
introduces multiple sessions for single target.

With this patch, it is possible to run puppeteer in headful mode
and open devtools over the automated pages without puppeteer losing
connection to the page.

lib/Launcher.js

@@ -37,6 +37,7 @@ const DEFAULT_ARGS = [
   '--disable-prompt-on-repost',
   '--disable-sync',
   '--enable-automation',
+  '--enable-devtools-experiments',
   '--metrics-recording-only',
   '--no-first-run',
   '--password-store=basic',