Add function for creating ASTC blitter

src/utils/SkTextureCompressor.cpp

Index: src/utils/SkTextureCompressor.cpp
diff --git a/src/utils/SkTextureCompressor.cpp b/src/utils/SkTextureCompressor.cpp
index 40c0d3e5e88714c80fca9a64661276a28c75f8b0..43d906aea57999df97195c769371a2eb5f8e553b 100644
--- a/src/utils/SkTextureCompressor.cpp
+++ b/src/utils/SkTextureCompressor.cpp
@@ -122,6 +122,9 @@ SkBlitter* CreateBlitterForFormat(int width, int height, void* compressedBuffer,
         case kR11_EAC_Format:
             return CreateR11EACBlitter(width, height, compressedBuffer);
 
+        case kASTC_12x12_Format:
+            return CreateASTCBlitter(width, height, compressedBuffer);
+
         default:
             return NULL;
     }