Implement onSkipScanlines() for bmp and wbmp

src/codec/SkBmpCodec.cpp

Index: src/codec/SkBmpCodec.cpp
diff --git a/src/codec/SkBmpCodec.cpp b/src/codec/SkBmpCodec.cpp
index cbba28c172de3e6bf440d0fda9824895764a7f7e..babb17d32e5902dab1c73c558f9c8247bd18f94e 100644
--- a/src/codec/SkBmpCodec.cpp
+++ b/src/codec/SkBmpCodec.cpp
@@ -546,6 +546,7 @@ SkBmpCodec::SkBmpCodec(const SkImageInfo& info, SkStream* stream,
     : INHERITED(info, stream)
     , fBitsPerPixel(bitsPerPixel)
     , fRowOrder(rowOrder)
+    , fSrcRowBytes(SkAlign4(compute_row_bytes(info.width(), fBitsPerPixel)))
 {}
 
 bool SkBmpCodec::onRewind() {
@@ -577,3 +578,12 @@ int SkBmpCodec::onGetScanlines(void* dst, int count, size_t rowBytes) {
     // Decode the requested rows
     return this->decodeRows(rowInfo, dst, rowBytes, this->options());
 }
+
+bool SkBmpCodec::skipRows(int count) {
+    const size_t bytesToSkip = count * fSrcRowBytes;
+    return this->stream()->skip(bytesToSkip) == bytesToSkip;
+}
+
+bool SkBmpCodec::onSkipScanlines(int count) {
+    return this->skipRows(count);
+}