Generalize compressed blitter into its own templated class

R=robertphillips@google.com

Author: krajcevski@google.com

Review URL: https://codereview.chromium.org/421593004
diff --git a/gyp/utils.gypi b/gyp/utils.gypi
index c90dbc5..c8fc3f0 100644
--- a/gyp/utils.gypi
+++ b/gyp/utils.gypi
@@ -87,6 +87,7 @@
         '<(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_Blitter.h',
         '<(skia_src_path)/utils/SkTextureCompressor_R11EAC.cpp',
         '<(skia_src_path)/utils/SkTextureCompressor_R11EAC.h',
         '<(skia_src_path)/utils/SkTextureCompressor_LATC.cpp',