This is a reland of ce240cc6fd
Original change's description:
> SkSurface asynchronous read APIs allow client to extend pixel lifetime
>
> Previously the pixel data passed to the client was only valid during
> the client's callback. This meant if the client wanted to defer
> processing of the data a copy was necessary.
>
> Now we pass an object to the callback and the pixel lifetime is tied
> to the lifetime of that object.
>
> The object may be holding a GPU transfer buffer mapped. We don't assume
> that the object will be released on the direct GrContext thread. So
> when the object is destroyed it posts a message to a new type,
> GrClientMappedBufferManager, hanging off the direct context. The direct
> context will periodically check for messages and unmap and then unref
> buffers so that they can be reused. Currently this is done in
> GrContext::performDeferredCleanup() and GrDrawingManager::flush().
>
> The old API is kept around for backwards compatibility but it is
> reimplemented as a bridge on top of the new mechanism.
>
> Also a utility function to SkImageInfo is added to directly make a new
> info with a specified dimensions rather than passing the width and
> height separately to makeWH().
>
> Bug: chromium:973403
> Bug: skia:8962
>
> Change-Id: Id5cf04235376170142a48e90d3ecd13fd021a2a6
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/245457
> Reviewed-by: Brian Osman <brianosman@google.com>
> Commit-Queue: Brian Salomon <bsalomon@google.com>
Bug: chromium:973403, skia:8962
Change-Id: I5cecd36276c8b6dc942cf549c7095db2df88530c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/245678
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
6fc04f88a8