Provide build target for angle_shader_translator sample. This is useful for building the sample within Chromium rather than in ANGLE's standalone build, which has other requirements like a full Visual Studio installation. BUG=angleproject:2095 Change-Id: I785d87ecb5166d8f640a5c8a5f321c3209017cc5 Reviewed-on: https://chromium-review.googlesource.com/553399 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>