Avoid trying to delete a non-existent file.

Avoid trying to delete a non-existent file.

BUG=368455
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=272726

[asanka, 2014-05-23 18:54:56]

Doesn't have tests since the observable effect should be the same if the
underlying filesystem isn't nuts.

[Randy Smith (Not in Mondays), 2014-05-23 19:05:20]

If you wanted to test it, you could, by calling Cancel(), recreating the file,
and then destroying the object.  That's effectively a regression test.  I'm
inclined in favor, but I could be talked out of it if you feel strongly.

https://codereview.chromium.org/296933016/diff/1/content/browser/download/bas...
File content/browser/download/base_file.cc (right):

https://codereview.chromium.org/296933016/diff/1/content/browser/download/bas...
content/browser/download/base_file.cc:185: Detach();
Hmmm.  I'm a bit uncomfortable with the abstractions in this file; in my mind
"detached_" should mean "don't have anything to do with the underlying file
anymore" and nothing should be allowed to happen in that state (with the
possible exception of Rename(), but even there, it seems like that's a good
invariant to keep).  I.e once you've detached, destruction should be a no-op. 
That's larger (if still minor) cleanup, so I'm not requesting that you do it. 
But I think I would like the detach to be after the conditional, below.

[asanka, 2014-05-23 19:34:44]

Added a test and moved the Detach to the end.

[Randy Smith (Not in Mondays), 2014-05-23 19:36:34]

lgtm

[asanka, 2014-05-23 21:41:17]

The CQ bit was checked by asanka@chromium.org

[commit-bot: I haz the power, 2014-05-23 21:42:38]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/asanka@chromium.org/296933016/60001

[commit-bot: I haz the power, 2014-05-24 00:56:14]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  mac_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/mac_chromium_rel/buil...)

[commit-bot: I haz the power, 2014-05-24 12:54:21]

Change committed as 272726