https://codereview.chromium.org/2654993004 moved the way we blacklist GPU Raster (Ganesh) to the GPU service.

With this change we are now running LayerTreeHostImpl::UpdateGpuRasterizationStatus and LayerTreeHostImpl::GetGpuRasterizationCapabilities on the UI compositor, and initializing a skia GrContext.  The decision is made that  gpu_rasterization_enabled for UI, but it actually is never used because we never call LTHI::SetHasGpuRasterizationTrigger(true) in the UI.

We should make the decision tree clearer here, and prevent initialization of GrContext, to reduce memory and related initialization time.