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This provides a mechanism for GLImage implementations to optimize
blit image to texture.

In the case of GLImageMemory, this allows us to upload directly
to the destination texture instead of first uploading to a temporary
texture copying pixels from this texture to the destination texture.

BUG=374962

Review URL: https://codereview.chromium.org/536353002

Cr-Commit-Position: refs/heads/master@{#293404}