windows opengl: Implement WinOpenGLSalGraphicsImpl::Init() too.

[Blind fix to fix build; real fix to follow after testing.]

Change-Id: Ic4cf2dc74ba4649a2453bc351cdc1d1fad59a0ca
Fix build.

Change-Id: Ibf5d1ccee155cc5807a1a125fde7a7243eab7585
windows opengl: We should actually use Init() from OpenGLSalGraphicsImpl.

Change-Id: I524883b0f0bbce9a8b6f893771f144feeee49934