gen.py can specify the name of the module

This will be the window variable assigned to when running in the
browser, without AMD or require.js.
Generate JS for integration test

* Remove naclbind.js from karma.conf.js. This will be automatically
  added to the generated JS.
* Modify naclbind-test to output the generated JS, and return it with
  the test code appended.
* glue.js now returns a module constructor instead of the module. This
  lets us pass in the nmf and mimetype.
Download Chromium from browser snapshots on Travis

The browser snapshot's version of Chrome include NaCl, but the one
installed by default on Travis doesn't.