Add ability to relinquish control of VkDevice and VkInstance lifetime to GrVkBackendContext

Change-Id: I355a8bf573a84b4ba7cbfeed60feec13e251b352
Reviewed-on: https://skia-review.googlesource.com/14303
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
2 files changed