Pass ImplFactory to Texture constructor This improves encapsulation inside the Texture class, and removes duplication of createTexture calls. This is a necessary step towards adding a shared "Data" structure to the Texture classes, following a similar pattern as for example the Framebuffer class. This patch also shares the same MockFactory class among different unit tests. BUG=angleproject:596 TEST=angle_unittests Change-Id: Ie8d3a9aa4ec35565d7ecbabb8c40e7b1ba068721 Reviewed-on: https://chromium-review.googlesource.com/340200 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>