WebView: Refactor AwDrawFnImpl

This CL refactors AwDrawFnImpl and creates AwVulkanContextProvider which
will be used to share vulkan objects with SkiaRenderer.

Bug: 939842
Change-Id: I6c8f4a628ea5e3f8b8cb26aaa902cdb3cb484fee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1512132
Commit-Queue: Peng Huang <penghuang@chromium.org>
Reviewed-by: Eric Karl <ericrk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#639729}
12 files changed