Create a scanline decoder without creating a codec

tests/CodexTest.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Resources.h"
 #include "SkBitmap.h"
 #include "SkCodec.h"
@@ skipping 77 matching lines @@
 
     bm.eraseColor(SK_ColorYELLOW);
 
     result =
         codec->getPixels(info, bm.getPixels(), bm.rowBytes(), NULL, NULL, NULL);
 
     REPORTER_ASSERT(r, result == SkCodec::kSuccess);
     // verify that re-decoding gives the same result.
     compare_to_good_digest(r, digest, bm);
 
-    SkAutoTDelete<SkScanlineDecoder> scanlineDecoder(codec->getScanlineDecoder(info));
+    stream.reset(resource(path));
+    SkAutoTDelete<SkScanlineDecoder> scanlineDecoder(
+            SkScanlineDecoder::NewFromStream(stream.detach()));
     if (supportsScanlineDecoding) {
         bm.eraseColor(SK_ColorYELLOW);
         REPORTER_ASSERT(r, scanlineDecoder);
 
-        // Regular decodes should not be affected by creating a scanline decoder
-        result = codec->getPixels(info, bm.getPixels(), bm.rowBytes(), NULL, NULL, NULL);
-        REPORTER_ASSERT(r, SkCodec::kSuccess == result);
-        compare_to_good_digest(r, digest, bm);
-
-        bm.eraseColor(SK_ColorYELLOW);
+        REPORTER_ASSERT(r, scanlineDecoder->start(info) == SkCodec::kSuccess);
 
         for (int y = 0; y < info.height(); y++) {
             result = scanlineDecoder->getScanlines(bm.getAddr(0, y), 1, 0);
             REPORTER_ASSERT(r, result == SkCodec::kSuccess);
         }
         // verify that scanline decoding gives the same result.
         compare_to_good_digest(r, digest, bm);
     } else {
         REPORTER_ASSERT(r, !scanlineDecoder);
     }
@@ skipping 166 matching lines @@
     test_empty(r, "empty_images/zero-embedded.ico");
     test_empty(r, "empty_images/zero-width.bmp");
     test_empty(r, "empty_images/zero-height.bmp");
     test_empty(r, "empty_images/zero-width.jpg");
     test_empty(r, "empty_images/zero-height.jpg");
     test_empty(r, "empty_images/zero-width.png");
     test_empty(r, "empty_images/zero-height.png");
     test_empty(r, "empty_images/zero-width.wbmp");
     test_empty(r, "empty_images/zero-height.wbmp");
 }