Make GrGpuCommandBuffer's methods take a GrRenderTargetProxy (rather than a GrRenderTarget)

In https://skia-review.googlesource.com/c/26363/ (Remove origin field from GrSurface) I just passed
an extra GrSurfaceOrigin parameter to all these methods. Besides being verbose this also led to
the "discard" method having an origin (to support the GrVkGpuCommandBuffer). It think this approach
is better and is plausible if the GrGpuCommandBuffer is viewed as an intermediary between the
GrProxy-based Ops and the Gpu.

In isolation this CL doesn't really show why we want to percolate the Proxy down. Once GrSurface
no longer has an origin a lot of the GrGpu methods need it passed in explicitly. By having the
GrGpuCommandBuffer get the proxy it can then pass the origin to GrGpu and removes a layer of
functions with an extra origin parameter.

Change-Id: Ie223fdee930171a32a5923155a0322e9a9c2aaa9
Reviewed-on: https://skia-review.googlesource.com/27980
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
10 files changed