Fixed issue with Ganesh texture bindings becoming corrupted

Corruption occurred when a canvas was used as the source of a texImage2D

BUG=368582

Review URL: https://codereview.chromium.org/268713009

git-svn-id: svn://svn.chromium.org/blink/trunk@173151 bbb929c8-8fbe-4397-9dbb-9b2b20218538