Revert of Disallow users modify canvas after it transfers control to offscreen (patchset #3 id:60001 of https://codereview.chromium.org/2323933004/ )

Reason for revert:
Breaks webkit_tests consistently after submit: https://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20Leak/builds/22857

Original issue's description:
> Disallow users modify canvas after it transfers control to offscreen
>
> After a canvas has transferred its control to Offscreen, we should not allow
> users to perform resizing, toDataURL, toBlob and getContext.
>
> BUG=563852
>
> Committed: https://crrev.com/85264448db0298f836e6d7bf95ad11134637e4ed
> Cr-Commit-Position: refs/heads/master@{#418114}

TBR=junov@chromium.org,xlai@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=563852

Review-Url: https://codereview.chromium.org/2335903003
Cr-Commit-Position: refs/heads/master@{#418188}
8 files changed