Remove all remaining non-test uses of std::stringstream.

Bug: webrtc:8982
Change-Id: I635a8545c46dc8c89663d64af351e22e65cbcb33
Reviewed-on: https://webrtc-review.googlesource.com/98880
Commit-Queue: Jonas Olsson <jonasolsson@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24715}
diff --git a/rtc_base/json.cc b/rtc_base/json.cc
index cc40bd6..f7716ab 100644
--- a/rtc_base/json.cc
+++ b/rtc_base/json.cc
@@ -14,25 +14,23 @@
 #include <limits.h>
 #include <stdlib.h>
 
-#include <sstream>
+#include "rtc_base/stringencode.h"
 
 namespace rtc {
 
 bool GetStringFromJson(const Json::Value& in, std::string* out) {
   if (!in.isString()) {
-    std::ostringstream s;
     if (in.isBool()) {
-      s << std::boolalpha << in.asBool();
+      *out = rtc::ToString(in.asBool());
     } else if (in.isInt()) {
-      s << in.asInt();
+      *out = rtc::ToString(in.asInt());
     } else if (in.isUInt()) {
-      s << in.asUInt();
+      *out = rtc::ToString(in.asUInt());
     } else if (in.isDouble()) {
-      s << in.asDouble();
+      *out = rtc::ToString(in.asDouble());
     } else {
       return false;
     }
-    *out = s.str();
   } else {
     *out = in.asString();
   }