Don't leak CopyResult textures.

When a CopyResult provides a TextureMailbox, the ReleaseCallback must
be called on the TextureMailbox when then client is done with the
CopyResult.

This change ensures that this happens. If the TextureMailbox is never
removed from the CopyResult, then the CopyResult destructor takes care
of it. Since the texture was never used, it uses a sync point of 0.

When the TextureMailbox is removed from the CopyResult, then RWHVAura
makes sure it calls the ReleaseCallback once it has the pixels it needs
in memory. Since the pixels are already available on the CPU, it can
use a sync point of 0 as well.

R=piman
BUG=263483

Review URL: https://chromiumcodereview.appspot.com/19990007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@213297 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed