tree 6abb5c61ad62b2a8e17985a662cbb05b1899dd73
parent 2481b8b71941914ed053400700299f20f7ff32fc
author reed <reed@google.com> 1438195492 -0700
committer Commit bot <commit-bot@chromium.org> 1438195492 -0700

SkImage_Raster's pixels are always immutable.

To make this work, we tag their pixelrefs as temporarily immutable, allowing
ourselves to restore the pixels to mutability only when the image drops away.

This should allow us to wobble back and forth between writing to the Surface
and reading from the Image without a COW, with the Surface seeing mutable
pixels and the Image seeing immutable pixels.

The big idea is, Image doesn't need forever-immutable pixels, it just needs
pixels that are immutable as long as it's alive.

BUG=skia:

patch from issue 804523002 at patchset 40001 (http://crrev.com/804523002#ps40001)

Review URL: https://codereview.chromium.org/1254383006