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This is a reland of db7626d6

Changes from the original: check if vk_context_provider not null.

Original change's description:
> Use GrShaderCache with Vulkan
>
> VulkanContextProvider is created before GrShaderCache and so cache
> wasn't pass to Skia via GrContextOptions.
>
> This CL defers init of GrContext in VulkanInProcessContextProvider to
> SharedContextState::InitializeGrContext to mitigate this.
>
> Use of cache itself is under feature flag for metrics comparison and
> a kill switch purpose.
>
> Bug: 1151031
> Change-Id: Idc410b9b557f7ca67164eb80d6a37a27ceb0f6d2
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2551245
> Reviewed-by: Peng Huang <penghuang@chromium.org>
> Commit-Queue: Vasiliy Telezhnikov <vasilyt@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#829651}

Bug: 1151031
Change-Id: Ibd4e7d55fdc56c1ea2cc0e82d6cc6c34459165c5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2554353Reviewed-by: Peng Huang <penghuang@chromium.org>
Commit-Queue: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830753}