Roll jsoncpp, drop dependency on Chromium overrides.

Roll jsoncpp, drop dependency on Chromium overrides.

This rolls jsoncpp to head, crucially past "Added missing includes for
std::istream." which has given us some grief in the past. And it's required to
build jsoncpp against libc++.

Vanilla jsoncpp works just fine for us, so no need for Chromium's overrides.
Like all DEPS, only tools depend on jsoncpp.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/3ba54fa0adb0a9bb81c09ef18d6f8cebea311a6f

[bungeman-skia, 2014-08-19 14:11:11]

lgtm, so long as everything keeps working

https://codereview.chromium.org/481823003/diff/1/gyp/jsoncpp.gyp
File gyp/jsoncpp.gyp (left):

https://codereview.chromium.org/481823003/diff/1/gyp/jsoncpp.gyp#oldcode35
gyp/jsoncpp.gyp:35:
'../third_party/externals/jsoncpp/include/json/assertions.h',
In general, I rather like having the header files listed so I can see them in
IDEs. On the other hand I must say that I have no plans to look at this project
(and we sure don't edit it), so it doesn't matter that much I suppose.

[mtklein, 2014-08-19 14:13:36]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-08-19 14:13:39]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/mtklein@chromium.org/481823003/1

[commit-bot: I haz the power, 2014-08-19 14:21:06]

Committed patchset #1 (1) as 3ba54fa0adb0a9bb81c09ef18d6f8cebea311a6f