Handle URLRequest::Read() returning false without an error or ERR_IO_PENDING.

Handle URLRequest::Read() returning false without an error or ERR_IO_PENDING.

This is a possible cause for a failure being seen in the field in the
associated bug; this change is a quick fix for that failure + UMA to
determine if the failure is real.

BUG=416639
R=mef@chromium.org
R=asvitkine@chromium.org

Committed: https://crrev.com/790eaaa7e24a27ad2d0f8fb8be458c6a2be8e84c
Cr-Commit-Position: refs/heads/master@{#296241}

[Randy Smith (Not in Mondays), 2014-09-23 16:31:37]

Misha: Could you review the primary change?  Alexei: Could you review the
histograms.xml change?  

This is one of our top crashers ATM, so I'd like to get the maybe-fix out ASAP.

[Alexei Svitkine (slow), 2014-09-23 16:39:21]

lgtm

[mef, 2014-09-23 17:23:43]

lgtm

[Randy Smith (Not in Mondays), 2014-09-23 17:25:08]

The CQ bit was checked by rdsmith@chromium.org

[commit-bot: I haz the power, 2014-09-23 17:59:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/597633002/1

[commit-bot: I haz the power, 2014-09-23 21:08:22]

Committed patchset #1 (id:1) as ac27abe0c8eb5c0232e694332266d1d774fab024

[commit-bot: I haz the power, 2014-09-23 21:09:12]

Patchset 1 (id:??) landed as
https://crrev.com/790eaaa7e24a27ad2d0f8fb8be458c6a2be8e84c
Cr-Commit-Position: refs/heads/master@{#296241}

[Ryan Hamilton, 2014-09-23 21:38:37]

rch@chromium.org changed reviewers:
+ rch@chromium.org

[Ryan Hamilton, 2014-09-23 21:38:38]

Drive-by nit...

https://codereview.chromium.org/597633002/diff/1/net/base/sdch_dictionary_fet...
File net/base/sdch_dictionary_fetcher.cc (right):

https://codereview.chromium.org/597633002/diff/1/net/base/sdch_dictionary_fet...
net/base/sdch_dictionary_fetcher.cc:206:
DCHECK_NE(current_request_->status().error(), OK);
Technically, the style guide prohibits "handling" failed DCHECKs.

http://www.chromium.org/developers/coding-style#TOC-CHECK-DCHECK-and-NOTREACHED-

That would suggest using something like DLOG(DFATAL) instead.

[Randy Smith (Not in Mondays), 2014-09-24 16:24:09]

On 2014/09/23 21:38:38, Ryan Hamilton wrote:
> Drive-by nit...
> 
>
https://codereview.chromium.org/597633002/diff/1/net/base/sdch_dictionary_fet...
> File net/base/sdch_dictionary_fetcher.cc (right):
> 
>
https://codereview.chromium.org/597633002/diff/1/net/base/sdch_dictionary_fet...
> net/base/sdch_dictionary_fetcher.cc:206:
> DCHECK_NE(current_request_->status().error(), OK);
> Technically, the style guide prohibits "handling" failed DCHECKs.
> 
>
http://www.chromium.org/developers/coding-style#TOC-CHECK-DCHECK-and-NOTREACHED-
> 
> That would suggest using something like DLOG(DFATAL) instead.

Fair enough; see https://codereview.chromium.org/599143002/

I was going to say "But if this isn't what's happening I want to revert the
change", but after some consideration, I don't; if it happens in the future, I
don't want browsers hanging.