GN: Add BUILD.gn file to third_party/jsoncpp

tools/gn/secondary/third_party/jsoncpp/BUILD.gn

+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+config("jsoncpp_config") {
+  include_dirs = [
+    "overrides/include",
+    "source/include",
+  ]
+}
+
+static_library("jsoncpp") {

[tfarina, 2014/06/11 16:28:41]

is there a reason for using static_library? if not, then I thin our preference
is to use source_set here.

[kjellander_chromium, 2014/06/11 16:49:56]

No reason, just that it was static_library in the .gyp. 
source_set seems to work fine.

+  configs += [ ":jsoncpp_config" ]
+  direct_dependent_configs = [ ":jsoncpp_config" ]
+
+  defines = [

[tfarina, 2014/06/11 16:28:41]

please, refert to
http://code.google.com/p/chromium/wiki/GNStyleGuide#Ordering_within_a_target for
how the ordering should be

[kjellander_chromium, 2014/06/11 16:49:56]

Sorry about that, I'm new here ;)

+    "JSON_USE_EXCEPTION=0",
+  ]
+
+  include_dirs = [
+    "source/src/lib_json",
+  ]
+
+  sources = [

[tfarina, 2014/06/11 16:28:41]

sources come before everything, move this at the top.

[kjellander_chromium, 2014/06/11 16:49:56]

Done.

+    "source/include/json/assertions.h",
+    "source/include/json/autolink.h",
+    "source/include/json/config.h",
+    "source/include/json/features.h",
+    "source/include/json/forwards.h",
+    "source/include/json/json.h",
+    "source/include/json/reader.h",
+    "overrides/include/json/value.h",

[tfarina, 2014/06/11 16:28:41]

could you sort this list.

[kjellander_chromium, 2014/06/11 16:49:56]

Done.

+    "source/include/json/writer.h",
+    "source/src/lib_json/json_batchallocator.h",
+    "overrides/src/lib_json/json_reader.cpp",
+    "source/src/lib_json/json_tool.h",
+    "overrides/src/lib_json/json_value.cpp",
+    "source/src/lib_json/json_writer.cpp",
+  ]
+}