Vulkan: Use push constant for masked clear color Storing the color in an uniform buffer, and updating it by vkCmdUpdateBuffer can hit a driver bug. Using vkCmdPushConstants instead can workaround this bug. Besides, push constant is expected to outperform memory-backed resource update according to the vkspec (section 13.2.6). Bug: angleproject:2547 Change-Id: I319cd8e07e0a1d0cb56005b78a46466d9fca436e Reviewed-on: https://chromium-review.googlesource.com/1067247 Commit-Queue: Jie A Chen <jie.a.chen@intel.com> Reviewed-by: Luc Ferron <lucferron@chromium.org>