Add missing overflow handling to base::RandInt().

Add missing overflow handling to base::RandInt().

The result of RandGenerator() could return a number as high as UINT_MAX,
so casting that to int and adding it to another int will in general overflow.
Overflow is undefined behavior for signed integers, so add some type casting
to make sure this doesn't happen.

The DCHECKs in RandInt() where catching that something fishy was going on
(see bug), so as test just call RandInt() a few times with large bounds.
This test made the DCHECK reliably fire without the fix.

BUG=548375
R=thestig@chromium.org

Committed: https://crrev.com/0a3852a7502c50ae8056090207c85c424804e706
Cr-Commit-Position: refs/heads/master@{#356939}

[Nico, 2015-10-29 15:47:22]

thakis@chromium.org changed reviewers:
+ thestig@chromium.org

[Lei Zhang, 2015-10-29 16:38:15]

lgtm

https://codereview.chromium.org/1419703005/diff/1/base/rand_util.cc
File base/rand_util.cc (right):

https://codereview.chromium.org/1419703005/diff/1/base/rand_util.cc#newcode26
base/rand_util.cc:26: static_cast<int>(min +
static_cast<int64>(base::RandGenerator(range)));
int64_t, and fix line 22 as well?

[Nico, 2015-10-29 16:46:45]

https://codereview.chromium.org/1419703005/diff/1/base/rand_util.cc
File base/rand_util.cc (right):

https://codereview.chromium.org/1419703005/diff/1/base/rand_util.cc#newcode26
base/rand_util.cc:26: static_cast<int>(min +
static_cast<int64>(base::RandGenerator(range)));
On 2015/10/29 16:38:15, Lei Zhang wrote:
> int64_t, and fix line 22 as well?

Done.

[Nico, 2015-10-29 16:46:50]

The CQ bit was checked by thakis@chromium.org

[Nico, 2015-10-29 16:46:50]

The patchset sent to the CQ was uploaded after l-g-t-m from thestig@chromium.org
Link to the patchset: https://codereview.chromium.org/1419703005/#ps20001
(title: "stdint hyyyyyyype")

[commit-bot: I haz the power, 2015-10-29 16:47:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1419703005/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1419703005/20001

[commit-bot: I haz the power, 2015-10-29 17:52:00]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-10-29 17:52:01]

Try jobs failed on following builders:
  linux_android_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_android_r...)

[commit-bot: I haz the power, 2015-10-29 20:44:56]

Patchset 2 (id:??) landed as
https://crrev.com/0a3852a7502c50ae8056090207c85c424804e706
Cr-Commit-Position: refs/heads/master@{#356939}