Modify PnaclHeaderTest to run w/ an empty PNaCl component dir.

Modify PnaclHeaderTest to run w/ an empty PNaCl component dir.

This helps check that the pexe fetch is able to happen before
the component files are accessed. Otherwise, if the component
files are accessed before the pexe fetch, then it will error
out early, and the PNaCl on-demand installation will not happen.

Followup to Justin's fix: https://codereview.chromium.org/453073002
I tested that without Justin's fix, this patch will make the test catch the error.

BUG=401755
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=289182

[teravest, 2014-08-12 20:55:40]

lgtm

Awesome, thanks.

[Nick Bray (chromium), 2014-08-12 22:28:57]

OWNERs LGTM without fully understanding it, but it sounds like some of the stuff
in the commit message should be in a comment?

[jvoung (off chromium), 2014-08-12 22:52:19]

On 2014/08/12 22:28:57, Nick Bray (chromium) wrote:
> OWNERs LGTM without fully understanding it, but it sounds like some of the
stuff
> in the commit message should be in a comment?

Thanks! I tried to clarify the comment a bit more.

[jvoung (off chromium), 2014-08-12 23:09:12]

The CQ bit was checked by jvoung@chromium.org

[commit-bot: I haz the power, 2014-08-12 23:52:35]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jvoung@chromium.org/467863002/20001

[commit-bot: I haz the power, 2014-08-13 03:24:19]

Change committed as 289182