Fixed race when gpu process crashes before transfer buffer is created.
Fixed race when gpu process crashes before transfer buffer is created.

Since the transfer buffer is created lazily it is possible for the
gpu process to crash before the transfer buffer is actually created.
In that case the command buffer helper correctly indicates that it is
not usable, but does not signify that the context has been lost.

If the command buffer is unusable, it should also indicate that the
context has been lost.

R=vmiura@chromium.org
BUG=467678

Review URL: https://codereview.chromium.org/1269993002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#341449}

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