Add GrStagingBufferManager and use GrGpuBuffers to manage caching.

With this change if a backend Gr*Gpu wants to using staging buffers
they just add a generic GrStagingBufferManager member object. This
object can be used to get slices of upload buffers. Then they just need
to implement the virtual for taking ownership of buffers during submit.

We rely on our GrResourceCache to handle caching and reuse of these

This change allows us to remove all other virtuals on GrGpu around
managing staging buffers.

Change-Id: I5db9a3c52133978ea89d6c0de440f434fbf91a51
Commit-Queue: Greg Daniel <>
Reviewed-by: Stephen White <>
21 files changed