change a stringstream over to stringbuilder
change a stringstream over to stringbuilder

Bug: webrtc:8982
Change-Id: I4d8605acd59926a5873bfc7ca4ce902854f2708e
Reviewed-on: https://webrtc-review.googlesource.com/64880
Commit-Queue: Jonas Olsson <7906496040a7ac5328c0e08cb0fb50d1a12c27fd@webrtc.org>
Reviewed-by: Karl Wiberg <2c708eb0a58047bf403399f50b3da33ffd2dd444@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#23095}
TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc