String builder is similar to SimpleStringBuilder, but the difference is
that StringBuilder is built around a std::string instance and supports
dynamic resizing.
Change-Id: I874d22e69e639ff9ef3d5929366f4ba71c545787
Bug: webrtc:8982
Reviewed-on: https://webrtc-review.googlesource.com/58980
Commit-Queue: Jonas Olsson <jonasolsson@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24526}