For current WEBGL_video_image implementation, VideoImage texture type translates to its
native texture type in blink layer.

A refactory for this implementation is required but is complicated and need much time.
Currently, we need a workaround in ANGLE to support this extension.

Current end2end tests can monitor this workaround well.

BUG=chromium:776222, angleproject:3889
Change-Id: I864bc2734cfffc8c5aea6166466767e3fb31c1c7
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1989864
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>