[Qtwebengine] Video texture streaming

[Mansoor C]

Hi All:

Here at BlackBerry we have been developing support for EGLImage based
video texture streaming for QtWebEngine/QNX. It adds a new
StreamVideoNode class similar to the existing YUVVideoNode class. It
also adds support for new cc::DrawQuad::STREAM_VIDEO_CONTENT material
in DelegatedFrameNode.

We have this working successfully in our QtWebEngine test app on QNX platform.

I have pushed a clean patch for gerrit review here:
https://codereview.qt-project.org/#change,78138

For now I have put Jocelyn and Arvid as reviewers. I am not sure who
else should be looking at it.

I have intentionally tried to keep changes localized to QtWebEngine -
and not mess with QSG APIs. But if there are better ways to implement
this, I am open to your suggestions.

Thanks,
Mansoor