Add the ability to decode a subset to SkCodec.

src/codec/SkCodec_libico.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 "SkCodec_libbmp.h"
 #include "SkCodec_libico.h"
 #include "SkCodec_libpng.h"
@@ skipping 211 matching lines @@
     return fEmbeddedCodecs->operator[](minIndex)->getInfo().dimensions();
 }
 
 /*
  * Initiates the Ico decode
  */
 SkCodec::Result SkIcoCodec::onGetPixels(const SkImageInfo& dstInfo,
                                         void* dst, size_t dstRowBytes,
                                         const Options& opts, SkPMColor* ct,
                                         int* ptr) {
+    if (opts.fSubset) {
+        // Subsets are not supported.
+        return kUnimplemented;
+    }
     // We return invalid scale if there is no candidate image with matching
     // dimensions.
     Result result = kInvalidScale;
     for (int32_t i = 0; i < fEmbeddedCodecs->count(); i++) {
         // If the dimensions match, try to decode
         if (dstInfo.dimensions() ==
                 fEmbeddedCodecs->operator[](i)->getInfo().dimensions()) {
 
             // Perform the decode
             result = fEmbeddedCodecs->operator[](i)->getPixels(dstInfo,
                     dst, dstRowBytes, &opts, ct, ptr);
 
             // On a fatal error, keep trying to find an image to decode
             if (kInvalidConversion == result || kInvalidInput == result ||
                     kInvalidScale == result) {
                 SkCodecPrintf("Warning: Attempt to decode candidate ico failed.\n");
                 continue;
             }
 
             // On success or partial success, return the result
             return result;
         }
     }
 
     SkCodecPrintf("Error: No matching candidate image in ico.\n");
     return result;
 }