Replace free isnan with std::isnan

Replace free isnan with std::isnan

isnan from cmath is not a free function, but part of the std namespace.
This worked before, but was changed in in glibc 2.23
https://sourceware.org/bugzilla/show_bug.cgi?id=19439.

BUG=595429
TEST=Chrome compiles with glibc 2.23

Committed: https://crrev.com/f46ba822df322dc98315eba4493382dc80bfc1c5
Cr-Commit-Position: refs/heads/master@{#385134}

[robwu, 2016-04-04 20:23:31]

rob@robwu.nl changed reviewers:
+ dbeam@chromium.org

[robwu, 2016-04-04 20:23:32]

Regarding https://codereview.chromium.org/1758573002#msg11

> https://chromium-cpp.appspot.com/ mentions <cmath> instead of <math.h>, don't
really know the difference myself...

math.h is a C header (and deprecated in C++) (C doesn't have namespaces).
cmath is roughly equivalent to including the symbols from math.h into the std
namespace.
The c++11 standard (depr.c.headers) allows but does not require both headers to
be equivalent (i.e. exporting symbols to the global AND the std namespaces).

[Dan Beam, 2016-04-04 23:57:44]

lgtm

[robwu, 2016-04-05 08:33:14]

The CQ bit was checked by rob@robwu.nl

[commit-bot: I haz the power, 2016-04-05 08:33:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1853263002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1853263002/1

[commit-bot: I haz the power, 2016-04-05 08:37:54]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-04-05 08:39:20]

Description was changed from

==========
Replace free isnan with std::isnan

isnan from cmath is not a free function, but part of the std namespace.
This worked before, but was changed in in glibc 2.23
https://sourceware.org/bugzilla/show_bug.cgi?id=19439.

BUG=595429
TEST=Chrome compiles with glibc 2.23
==========

to

==========
Replace free isnan with std::isnan

isnan from cmath is not a free function, but part of the std namespace.
This worked before, but was changed in in glibc 2.23
https://sourceware.org/bugzilla/show_bug.cgi?id=19439.

BUG=595429
TEST=Chrome compiles with glibc 2.23

Committed: https://crrev.com/f46ba822df322dc98315eba4493382dc80bfc1c5
Cr-Commit-Position: refs/heads/master@{#385134}
==========

[commit-bot: I haz the power, 2016-04-05 08:39:22]

Patchset 1 (id:??) landed as
https://crrev.com/f46ba822df322dc98315eba4493382dc80bfc1c5
Cr-Commit-Position: refs/heads/master@{#385134}