Add subsetting to SkScanlineDecoder

src/codec/SkBmpCodec.cpp

Index: src/codec/SkBmpCodec.cpp
diff --git a/src/codec/SkBmpCodec.cpp b/src/codec/SkBmpCodec.cpp
index 1aa43f583cbcc2a536c6f1b8e8fb6dd15acb7be5..0222c8ce9fbb2ec2ef809063089bb00beedcaa17 100644
--- a/src/codec/SkBmpCodec.cpp
+++ b/src/codec/SkBmpCodec.cpp
@@ -564,10 +564,6 @@ uint32_t SkBmpCodec::computeNumColors(uint32_t numColors) {
 
 SkCodec::Result SkBmpCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
         const SkCodec::Options& options, SkPMColor inputColorPtr[], int* inputColorCount) {
-    if (options.fSubset) {
-        // Subsets are not supported.
-        return kUnimplemented;
-    }
     if (!conversion_possible(dstInfo, this->getInfo())) {
         SkCodecPrintf("Error: cannot convert input type to output type.\n");
         return kInvalidConversion;