Add preliminary ASTC encoder

R=robertphillips@google.com

Author: krajcevski@google.com

Review URL: https://codereview.chromium.org/417933005
diff --git a/gyp/utils.gypi b/gyp/utils.gypi
index 9efa280..c90dbc5 100644
--- a/gyp/utils.gypi
+++ b/gyp/utils.gypi
@@ -85,6 +85,8 @@
         '<(skia_src_path)/utils/SkRTConf.cpp',
         '<(skia_src_path)/utils/SkTextureCompressor.cpp',
         '<(skia_src_path)/utils/SkTextureCompressor.h',
+        '<(skia_src_path)/utils/SkTextureCompressor_ASTC.cpp',
+        '<(skia_src_path)/utils/SkTextureCompressor_ASTC.h',
         '<(skia_src_path)/utils/SkTextureCompressor_R11EAC.cpp',
         '<(skia_src_path)/utils/SkTextureCompressor_R11EAC.h',
         '<(skia_src_path)/utils/SkTextureCompressor_LATC.cpp',