Pass compressed blitters to our mask drawing algorithm

src/utils/SkTextureCompressor_ASTC.cpp

Index: src/utils/SkTextureCompressor_ASTC.cpp
diff --git a/src/utils/SkTextureCompressor_ASTC.cpp b/src/utils/SkTextureCompressor_ASTC.cpp
index 8efffdfc9e8f04e035009bfc17a207ab8297758c..29d9725822f029e3563c9c480c207b579541f506 100644
--- a/src/utils/SkTextureCompressor_ASTC.cpp
+++ b/src/utils/SkTextureCompressor_ASTC.cpp
@@ -280,6 +280,20 @@ bool CompressA8To12x12ASTC(uint8_t* dst, const uint8_t* src, int width, int heig
 }
 
 SkBlitter* CreateASTCBlitter(int width, int height, void* outputBuffer) {
+    if ((width % 12) != 0 || (height % 12) != 0) {
+        return NULL;
+    }
+
+    // Memset the output buffer to an encoding that decodes to zero...
+    // In the case of ASTC, if everything index is zero, then the interpolated value
+    // will decode to zero provided we have the right header. We use the encoding
+    // from recognizing all zero blocks from above.
+    const int nBlocks = (width * height / 144);
+    uint8_t *dst = reinterpret_cast<uint8_t *>(outputBuffer);
+    for (int i = 0; i < nBlocks; ++i) {
+        send_packing(&dst, SkTEndian_SwapLE64(0x0000000001FE000173ULL), 0);
+    }
+
     return new
         SkTCompressedAlphaBlitter<12, 16, CompressA8ASTCBlockVertical>
         (width, height, outputBuffer);