Clean up specifying colors and texture scale in MipmapTest Remove unnecessary scale parameter from MipmapTestES3, and use the GLColor class and EXPECT_PIXEL_COLOR_EQ instead of EXPECT_PIXEL_EQ for greater readability. BUG=angleproject:596 TEST=angle_end2end_tests Change-Id: I79c30ce85be5d554d89197f8f1ce7ab0c51c11b6 Reviewed-on: https://chromium-review.googlesource.com/344513 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>