Add preliminary ASTC encoder

src/utils/SkTextureCompressor_ASTC.h

Index: src/utils/SkTextureCompressor_ASTC.h
diff --git a/src/utils/SkTextureCompressor_ASTC.h b/src/utils/SkTextureCompressor_ASTC.h
new file mode 100644
index 0000000000000000000000000000000000000000..152fc62f16e2b1b476ad53dde8d54c184c62299d
--- /dev/null
+++ b/src/utils/SkTextureCompressor_ASTC.h
@@ -0,0 +1,24 @@
+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkTextureCompressor_ASTC_DEFINED
+#define SkTextureCompressor_ASTC_DEFINED
+
+#include <stdint.h>
+
+// Forward declare
+class SkBlitter;
+
+namespace SkTextureCompressor {
+
+    bool CompressA8To12x12ASTC(uint8_t* dst, const uint8_t* src,
+                               int width, int height, int rowBytes);
+
+    SkBlitter* CreateASTCBlitter(int width, int height, void* outputBuffer);
+}
+
+#endif  // SkTextureCompressor_ASTC_DEFINED