Use preallocated space for default vertex and index buffer sizes

Change-Id: I64450701f51621347f613251d082e159a04ec7b3
Reviewed-on: https://skia-review.googlesource.com/c/163720
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
8 files changed