commit d06920a29fe11c68bde2b93948ec99f277bb8459
author scroggo <scroggo@google.com> Thu Apr 14 11:40:48 2016 -0700
committer Commit bot <commit-bot@chromium.org> Thu Apr 14 11:40:48 2016 -0700
tree ebe20f9cd4b63247d52fc555ca620accec5eabdd
parent d5f2e2e7429b643943d2f8a532c65e2498223b5b

Fixes for SkRWBuffer

Do not call SkBufferHead::validate in SkROBuffer's destructor, which
may be called in a separate thread from SkRWBuffer::append. validate()
reads SkBufferBlock::fUsed, and append() writes to it, resulting in
a data race.

Update some comments to be more clear about how it is safe to use
these classes across threads.

Test the readers in separate threads.

In addition, make sure it is safe to create a reader even when no
data has been appended. Add tests for this case.

Mark a parameter to SkBufferHead::validate() as const, reflecting
its use.

BUG=chromium:601578
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1871953002

Review URL: https://codereview.chromium.org/1871953002