Add the ability to decode a subset to SkCodec.

src/codec/SkCodec_wbmp.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.h"
 #include "SkColorPriv.h"
 #include "SkStream.h"
@@ skipping 85 matching lines @@
 SkWbmpCodec::SkWbmpCodec(const SkImageInfo& info, SkStream* stream)
     : INHERITED(info, stream) {}
 
 SkEncodedFormat SkWbmpCodec::onGetEncodedFormat() const {
     return kWBMP_SkEncodedFormat;
 }
 
 SkCodec::Result SkWbmpCodec::onGetPixels(const SkImageInfo& info,
                                          void* pixels,
                                          size_t rowBytes,
-                                         const Options&,
+                                         const Options& options,
                                          SkPMColor ctable[],
                                          int* ctableCount) {
     SkCodec::RewindState rewindState = this->rewindIfNeeded();
     if (rewindState == kCouldNotRewind_RewindState) {
         return kCouldNotRewind;
     } else if (rewindState == kRewound_RewindState) {
         (void)read_header(this->stream(), NULL);
     }
+    if (options.fSubset) {
+        // Subsets are not supported.
+        return kUnimplemented;
+    }
     if (info.dimensions() != this->getInfo().dimensions()) {
         return kInvalidScale;
     }
     ExpandProc proc = NULL;
     switch (info.colorType()) {
         case kGray_8_SkColorType:
             proc = expand_bits_to_T<uint8_t, bit_to_grayscale>;
             break;
         case kN32_SkColorType:
             proc = expand_bits_to_T<SkPMColor, bit_to_pmcolor>;
@@ skipping 32 matching lines @@
     SkAutoTDelete<SkStream> streamDeleter(stream);
     SkISize size;
     if (!read_header(stream, &size)) {
         return NULL;
     }
     SkImageInfo info =
             SkImageInfo::Make(size.width(), size.height(), kGray_8_SkColorType,
                               kOpaque_SkAlphaType);
     return SkNEW_ARGS(SkWbmpCodec, (info, streamDeleter.detach()));
 }