Implement onSkipScanlines() for bmp and wbmp

src/codec/SkWbmpCodec.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 "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 163 matching lines @@
     for (int y = 0; y < count; ++y) {
         if (!this->readRow(fSrcBuffer.get())) {
             return y;
         }
         fSwizzler->swizzle(dstRow, fSrcBuffer.get());
         dstRow = SkTAddOffset<void>(dstRow, dstRowBytes);
     }
     return count;
 }
 
+bool SkWbmpCodec::onSkipScanlines(int count) {
+    const size_t bytesToSkip = count * fSrcRowBytes;
+    return this->stream()->skip(bytesToSkip) == bytesToSkip;
+}
+
 SkCodec::Result SkWbmpCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
         const Options& options, SkPMColor inputColorTable[], int* inputColorCount) {
     if (options.fSubset) {
         // Subsets are not supported.
         return kUnimplemented;
     }
 
     if (!valid_alpha(dstInfo.alphaType(), this->getInfo().alphaType())) {
         return kInvalidConversion;
     }
 
     // Fill in the color table
     setup_color_table(dstInfo.colorType(), inputColorTable, inputColorCount);
 
     // Copy the color table to a pointer that can be owned by the scanline decoder
     if (kIndex_8_SkColorType == dstInfo.colorType()) {
         fColorTable.reset(new SkColorTable(inputColorTable, 2));
     }
 
     // Initialize the swizzler
     fSwizzler.reset(this->initializeSwizzler(dstInfo, get_color_ptr(fColorTable.get()), options));
     if (nullptr == fSwizzler.get()) {
         return kInvalidConversion;
     }
 
     fSrcBuffer.reset(fSrcRowBytes);
 
     return kSuccess;
 }