switch over to computeByteSize for image buffer calcs

The older apis (e.g. getSize) are deprecated.

old: getSize()
- computed height * rowBytes, even for last row
- not check for overflow

new: computeByteSize()
- computes (height - 1)* rowBytes + width*pixel_size (skip last padding)
- safely returns max_size_t on overflow

TBR=

Bug: 
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_site_isolation
Change-Id: I1ba4bbec58a25c12ae69c368a6da7c8f84056ec7
Reviewed-on: https://chromium-review.googlesource.com/710395
Commit-Queue: Mike Reed <[email protected]>
Reviewed-by: Reilly Grant <[email protected]>
Reviewed-by: Will Harris <[email protected]>
Reviewed-by: Antoine Labour <[email protected]>
Reviewed-by: Nico Weber <[email protected]>
Reviewed-by: Florin Malita <[email protected]>
Cr-Commit-Position: refs/heads/master@{#508477}
27 files changed