Use StringPrintf() instead of std::to_string().
Use StringPrintf() instead of std::to_string().

Android NDK r15 lacks the latter...

Change-Id: Iace89318c96065cd156aef5a6e6718edbffa1a6b
Reviewed-on: https://code-review.googlesource.com/19550
Reviewed-by: Paul Wankadia <62d4e38bb1380f055ec4b899baa75e52af09c5f7@google.com>

google/re2,google/re2,google/re2,google/re2,google/re2