Fix GPU process crash in ChromecastShellBrowserTest.EmptyTest

Fix GPU process crash in ChromecastShellBrowserTest.EmptyTest

Using --disable-gpu to fix the GPU process crash.  Unfortunately this exposed
a different crash in our teardown process.  For now, I've removed the test code
that shuts down render processes.  The problem with this is Chromecast code
reacts to the render process dying and tries to start the error screen just as
it's about to be shut down.  This ultimately leads to a crash.

Chromecast code shuts down the render processes itself, so I don't believe we
need the FastShutdownIfPossible calls in this test.

BUG=

Committed: https://crrev.com/dfffeb6a4d6f834ef553fcdbaf0367df8b5437c0
Cr-Commit-Position: refs/heads/master@{#311801}

[halliwell, 2015-01-15 19:55:43]

halliwell@chromium.org changed reviewers:
+ byungchul@chromium.org, gunsch@chromium.org

[gunsch, 2015-01-15 22:55:36]

lgtm

[gunsch, 2015-01-15 22:55:37]

lgtm

[byungchul, 2015-01-15 23:08:08]

lgtm

[halliwell, 2015-01-15 23:08:58]

The CQ bit was checked by halliwell@chromium.org

[commit-bot: I haz the power, 2015-01-15 23:09:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/818803004/1

[commit-bot: I haz the power, 2015-01-16 00:56:51]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-16 00:58:13]

Patchset 1 (id:??) landed as
https://crrev.com/dfffeb6a4d6f834ef553fcdbaf0367df8b5437c0
Cr-Commit-Position: refs/heads/master@{#311801}