DCHECK written counts from fwrite to fix unused return result.

DCHECK written counts from fwrite to fix unused return result.

These checks were lost in refs/heads/master@{#294801}: https://codereview.chromium.org/541763002.

BUG=382975
TEST=Compiling does not warn about an unused result.

Committed: https://crrev.com/230430abd55cab91d2d5e2c7a4b843ae0b89472b
Cr-Commit-Position: refs/heads/master@{#295195}

[flackr, 2014-09-16 21:19:55]

flackr@chromium.org changed reviewers:
+ caseq@chromium.org, pkotwicz@chromium.org

[flackr, 2014-09-16 21:19:56]

PTAL, adds back DCHECK's that the return from fwrite is used which were lost
when this code was refactored. Alternately we could explicitly ignore_result.

[pkotwicz, 2014-09-16 21:30:30]

LGTM. You may want to use BUG=382975

[flackr, 2014-09-16 22:29:06]

flackr@chromium.org changed reviewers:
+ dsinclair@chromium.org

[flackr, 2014-09-16 22:29:23]

+dsinclair for OWNER approval.

[dsinclair, 2014-09-16 23:05:26]

The CQ bit was checked by dsinclair@chromium.org

[dsinclair, 2014-09-16 23:05:27]

lgtm

[commit-bot: I haz the power, 2014-09-16 23:07:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/573963007/1

[commit-bot: I haz the power, 2014-09-17 00:52:13]

Committed patchset #1 (id:1) as ec0df5f6c910b0946b5dd845e664d1a4440df71e

[commit-bot: I haz the power, 2014-09-17 00:52:29]

Patchset 1 (id:??) landed as
https://crrev.com/230430abd55cab91d2d5e2c7a4b843ae0b89472b
Cr-Commit-Position: refs/heads/master@{#295195}

[caseq, 2014-09-17 07:35:21]

Please note I omitted DCHECKs on purpose -- these are meant to state invariants.
The success of an I/O operation is not an invariant. The style guide is pretty
explicit on that:
http://www.chromium.org/developers/coding-style#TOC-CHECK-DCHECK-and-NOTREACHED-

Use DCHECK() or NOTREACHED() as assertions, e.g. to document pre- and
post-conditions. A DCHECK() means "this condition must always be true", not
"this condition is normally true, but perhaps not in exceptional cases." Things
like disk corruption or strange network errors are examples of exceptional
circumstances that nevertheless should NOT result in DCHECK() failure.