Add drawImage() originClean() getSecurityOrigin() to OffscreenCanvas

This patch adds m_originClean flag to OffscreenCanvas and
 ensures that OCRC2D also use the value of this flag instead
of keeping its own redundant copy. It propagates the value of
 originClean in transferToImageBitmap().

This patch also expose drawImage() API functions in ORCRC2D in workers.

BUG=563870, 563856

Review-Url: https://codereview.chromium.org/1928043002
Cr-Commit-Position: refs/heads/master@{#391002}
20 files changed