chrome testing fixes

1. Starting with Chrome 29 (canary), chromedriver no longer works.
   Instead we need chromedriver2 (which also works with earlier Chromes).

2. Chromedriver2 no longer supports the old way of setting
   Chrome options with capability names like "chrome.binary".
   We need to use the ChromeOptions object.

3. This adds a new flag test.chrome.args which lets you specify a
   semicolon-separated list of command-line args for Chrome.

   In particular "--js-flags=--harmony" will turn on experimental js
   features.  (Note, if you look at about:flags, "experimental js"
   will show as off. The "experimental js" flag causes Chrome to pass
   --harmony to the js engine, and it doesn't reflect the current
   state of the js engine. There isn't a command-line arg that will
   set the "experimental js" flag itself.)

4. I'm updating selenium to the latest 2.33 for no reason, it's not
   relevant to any of the Chrome problems.  (The jar isn't in this
   CL because codereview gets confused by the large binary file.)

I'll update the wiki page on testing after committing this.

[kpreid2, 2013-05-30 01:06:40]

LGTM

[felix8a, 2013-05-30 06:10:14]

@r5429