Fixing bad error return code in html5fs remove/unlink/rmdir.

Fixing bad error return code in html5fs remove/unlink/rmdir.

Creating a FileRef does not check if the file exists or not.
We had assumed that if a FileRef could be created that
the file or directory in question exists.
Instead look at the result code from Query and possibly
return ENOENT if it turns out the file or diretory does not
exist.

BUG=None
TEST=nacl_io_tests
R=sbc@chromium.org

Committed: https://crrev.com/c27b19192a297c1b81da98e728305d4a5009a081
Cr-Commit-Position: refs/heads/master@{#314582}

[bradn, 2015-02-04 17:09:19]

bradnelson@google.com changed reviewers:
+ slegall@chromium.org

[Sam Clegg, 2015-02-04 17:28:04]

lgtm

[bradn, 2015-02-04 17:42:24]

The CQ bit was checked by bradnelson@google.com

[commit-bot: I haz the power, 2015-02-04 17:43:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/899003002/1

[commit-bot: I haz the power, 2015-02-04 18:06:53]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-04 18:07:49]

Patchset 1 (id:??) landed as
https://crrev.com/c27b19192a297c1b81da98e728305d4a5009a081
Cr-Commit-Position: refs/heads/master@{#314582}