Change 0 extraSize allocation behavior for SkArenaAlloc

Change the behavior from allocating only the memory needed for T.
to an exponential growth starting at 1024.

Change-Id: Id37e0fb9e269feebf669ebc73f9e26dcd0589452
Reviewed-on: https://skia-review.googlesource.com/c/162102
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Herb Derby <herb@google.com>
2 files changed