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When sharing textures in mailboxes using MailboxManagerSync
there's an optimization that if textures are not updated then
there is no need to share it again. However the code that
checks whether textures are updated ignores the cleared
state, causing shared texture to remain uncleared
indefinitely.

Fix by check the cleared state. And add a unit test.

BUG=453199

Review URL: https://codereview.chromium.org/890453002

Cr-Commit-Position: refs/heads/master@{#313814}