Specify texture LOD in compute shader on D3D backend D3D does not define LOD in compute shader, so Sample() is not supported, try to use SampleLevel(). Bug: angleproject:2756 TEST=angle_end2end_tests.ComputeShaderTest .TextureFunction/ES3_1_D3D11 dEQP.GLES31/functional_image_load_store_2d_store* Change-Id: I63e707d2b56e807cfe766cc21bc6b0819982ce80 Reviewed-on: https://chromium-review.googlesource.com/c/1379672 Commit-Queue: Xinghua Cao <xinghua.cao@intel.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>