The GraphicsSurface class already has a copyToGLTexture function. The counterpart for drawing onto the GraphicsSurface is still missing. This should allow uploading a texture that was rendered in an fbo to the GraphicsSurface / ShareableSurface.
see: https://bugs.webkit.org/show_bug.cgi?id=87725 This was implemented in r118987 as GraphicsSurface::copyFromFramebuffer().