Use Fibonacci instead of 2^n for block growth.

Chrome on android showed an increase of 5% memory use when 2^n block
growth was introduced. Use Fibonacci instead.

BUG=chromium:699130

Change-Id: I228d66385c63d487e72db46356f44e9efb5fa0f3
Reviewed-on: https://skia-review.googlesource.com/9447
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
2 files changed