SkXbyak basics

A little JIT proof of concept for SkRasterPipeline, using xbyak, which is a header-only assembler.  It's x86-only, but supports x86 very thoroughly, and it's very user friendly (at least as far as assembler libraries go...).

CQ_INCLUDE_TRYBOTS=skia.primary:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD

Change-Id: Ie17e562b0f3fff5914041badfb2c1fe4f86efab8
Reviewed-on: https://skia-review.googlesource.com/5730
Reviewed-by: Herb Derby <herb@google.com>
Reviewed-by: Heather Miller <hcm@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
diff --git a/DEPS b/DEPS
index 60c7ce9..0eb3193 100644
--- a/DEPS
+++ b/DEPS
@@ -42,6 +42,9 @@
 
   # microhttpd for skiaserve
   "third_party/externals/microhttpd" : "https://android.googlesource.com/platform/external/libmicrohttpd@748945ec6f1c67b7efc934ab0808e1d32f2fb98d",
+
+  # TODO: mirror to skia.googlesource.com
+  "third_party/externals/xbyak" : "https://github.com/herumi/xbyak",
 }
 
 recursedeps = [ "common" ]