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This CL makes sure that DisplayResourceProvider return resources only
when GPU Thread is available to make sure ReleaseImageContexts will
complete in finite time.

This doesn't change anything for Chrome where GPU Thread is always
available, but on webview RenderThread that used for gpu access during
composition is available only during specific times (init, dtor,
DrawAndSwap)

Bug: 1068716

Change-Id: I8fa482ab7399d6ce7639c1d76187be86ce152059
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2138551
Commit-Queue: Vasiliy Telezhnikov <vasilyt@chromium.org>
Reviewed-by: Jonathan Backer <backer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#757967}