Upgrade jsoncpp to 1.9.4

Bug: 170642246
Change-Id: Id1fae5a1b6421117f923c616718ee4b3571231e0
diff --git a/include/json/forwards.h b/include/json/forwards.h
index 84a26cd..affe33a 100644
--- a/include/json/forwards.h
+++ b/include/json/forwards.h
@@ -1,4 +1,4 @@
-// Copyright 2007-2010 Baptiste Lepilleur
+// Copyright 2007-2010 Baptiste Lepilleur and The JsonCpp Authors
 // Distributed under MIT license, or public domain if desired and
 // recognized in your jurisdiction.
 // See file LICENSE for detail or copy at http://jsoncpp.sourceforge.net/LICENSE
@@ -13,17 +13,23 @@
 namespace Json {
 
 // writer.h
+class StreamWriter;
+class StreamWriterBuilder;
+class Writer;
 class FastWriter;
 class StyledWriter;
+class StyledStreamWriter;
 
 // reader.h
 class Reader;
+class CharReader;
+class CharReaderBuilder;
 
-// features.h
+// json_features.h
 class Features;
 
 // value.h
-typedef unsigned int ArrayIndex;
+using ArrayIndex = unsigned int;
 class StaticString;
 class Path;
 class PathArgument;
@@ -31,12 +37,6 @@
 class ValueIteratorBase;
 class ValueIterator;
 class ValueConstIterator;
-#ifdef JSON_VALUE_USE_INTERNAL_MAP
-class ValueMapAllocator;
-class ValueInternalLink;
-class ValueInternalArray;
-class ValueInternalMap;
-#endif // #ifdef JSON_VALUE_USE_INTERNAL_MAP
 
 } // namespace Json