Include <string> and <istream> outside __pnacl__.

Fixes webrtc/ Debug build with libc++ which failed to link std::getline
as this is defined in <istream>. <iostream> causes static initializers
and shouldn't be necessary.

Also adds to README.chromium that the overrides are used too get rid of
static initializers and to build on libc++.

R=thakis@chromium.org
TBR=ronghuawu@chromium.org
BUG=webrtc:3739

Review URL: https://codereview.chromium.org/552013004

Cr-Commit-Position: refs/heads/master@{#293954}

third_party/jsoncpp/README.chromium

@@ -6,5 +6,9 @@ License File: LICENSE
 Security Critical: yes
 
 Description:
-The libjingle/webrtc/liblouis_nacl uses jsoncpp for signaling message serialization and deserialization.
+The libjingle/webrtc/liblouis_nacl uses jsoncpp for signaling message
+serialization and deserialization.
 
+Local modifications:
+The overrides are used to eliminate static initializers in json_value.cpp and
+json_reader.cpp adds includes for <string> and <istream> to build on libc++.

third_party/jsoncpp/overrides/src/lib_json/json_reader.cpp

@@ -14,16 +14,8 @@
 #include <cassert>
 #include <cstring>
 #include <stdexcept>
-#ifdef __pnacl__
-// This file uses the following headers (at least in Reader::parse), but
-// the upstream version doesn't include them because iostream pulls in
-// static initializers.  This breaks the PNaCl build because it uses
-// libc++ which declares getline in <string> (as per the C++ standard)
-// but defines it in <iostream>. The code therefore fails linking, which
-// these includes fix.
 #include <string>
-#include <iostream>
-#endif
+#include <istream>
 
 #if _MSC_VER >= 1400 // VC++ 8.0
 #pragma warning( disable : 4996 )   // disable warning about strdup being deprecated.