windows opengl: Instantiate OpenGLSalBitmap even on Windows.

Change-Id: I2229141cc12ad7bc9fccfd6e2c7fec44ac4f6284
windows opengl: Make sure we don't reach the slow parts of the code.

Change-Id: I2a4d1bd294d1d88651c8556091f5453ef0aa5293
vcl: Use the fast path for rendering.

There was a discrepancy between the comment and the code; and I believe the
comment was right, and the code wrong - so adapted the code accordingly.

[I guess we will want to kill this condition for good when rendering via
OpenGL at some stage; the assert() will tell us ;-)]

Change-Id: I651261373068e975004c898b2a930c602c158b64