Fix CharsetUtf8PerfTest.

The test performed a lot of repetitions of the same append call with a buffer that kept being extended which resulted in OOM errors, but now we use a new buffer each time.

Test: atest CharsetUtf8PerfTest
Bug: 235455275
Change-Id: I10427d315a6d0b45394c74d0c8642f0c085ceb07
1 file changed