Destroy SkScanlineDecoder in the SkCodec subclass destructors

tests/CodexTest.cpp

Index: tests/CodexTest.cpp
diff --git a/tests/CodexTest.cpp b/tests/CodexTest.cpp
index 5c969908b9ecb4122ba604b05623e9442d558f3a..0edd3cf907d62159e0ba5ff00de4288453ab59dd 100644
--- a/tests/CodexTest.cpp
+++ b/tests/CodexTest.cpp
@@ -72,6 +72,10 @@ static void check(skiatest::Reporter* r,
     if (supportsScanlineDecoding) {
         bm.eraseColor(SK_ColorYELLOW);
         REPORTER_ASSERT(r, scanlineDecoder);
+
+        // Regular decodes should be disabled after creating a scanline decoder
+        result = codec->getPixels(info, bm.getPixels(), bm.rowBytes(), NULL, NULL, NULL);
+        REPORTER_ASSERT(r, SkImageGenerator::kInvalidParameters == result);
         for (int y = 0; y < info.height(); y++) {
             result = scanlineDecoder->getScanlines(bm.getAddr(0, y), 1, 0);
             REPORTER_ASSERT(r, result == SkImageGenerator::kSuccess);