Removed VertexShader and FragmentShader in favor of using a single Shader object
Used VertexShaderD3D and FragmentShaderD3D directly when appropriate.

BUG=angle:731
Change-Id: Ib1ffdf85ee0bfa7c88bb9ddb1029ccbd63a9dbe1
Reviewed-on: https://chromium-review.googlesource.com/213840Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Brandon Jones <bajones@chromium.org>