Add timing SkCodec to nanobench.

bench/DecodingBench.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 "DecodingBench.h"
 #include "SkData.h"
 #include "SkImageDecoder.h"
@@ skipping 23 matching lines @@
             colorName = "Alpha8";
             break;
         default:
             colorName = "Unknown";
     }
     fName.printf("Decode_%s_%s", baseName.c_str(), colorName);
     
     // Perform setup for the decode
     SkAutoTUnref<SkData> encoded(SkData::NewFromFileName(path.c_str()));
     fStream.reset(new SkMemoryStream(encoded));
-    fDecoder.reset(SkImageDecoder::Factory(fStream.get()));
+#ifdef SK_DEBUG
+    // Ensure that we can create a decoder.
+    SkAutoTDelete<SkImageDecoder> decoder(SkImageDecoder::Factory(fStream.get()));
+    SkASSERT(decoder != NULL);
+#endif
 }
 
 const char* DecodingBench::onGetName() {
     return fName.c_str();
 }
 
 bool DecodingBench::isSuitableFor(Backend backend) {
     return kNonRendering_Backend == backend;
 }
 
 void DecodingBench::onDraw(const int n, SkCanvas* canvas) {
     SkBitmap bitmap;
+    SkAutoTDelete<SkImageDecoder> decoder;
+    SkAutoTDelete<SkStreamRewindable> stream;
     for (int i = 0; i < n; i++) {
-        fStream->rewind();
-        fDecoder->decode(fStream, &bitmap, fColorType,
-                         SkImageDecoder::kDecodePixels_Mode);
+        // duplicate the stream and create a new decoder to mimic the behavior of CodecBench.
+        stream.reset(fStream->duplicate());
+        decoder.reset(SkImageDecoder::Factory(stream));
+        decoder->decode(stream, &bitmap, fColorType,
+                        SkImageDecoder::kDecodePixels_Mode);
     }
 }