Cleanup resource flags

Converts GrResourceProvider::Flags and GrResourceCache::ScratchFlags
to "enum class" and fixes a case where we were accidentally using the
wrong type of flag. Makes sure to allocate GrSWMaskHelper proxies with
kNoPendingIO.

Bug: skia:8351
Change-Id: Ibcaa26314a53d0cb31ae22915ab94ab0fc07e76d
Reviewed-on: https://skia-review.googlesource.com/157280
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
25 files changed