Add subsetting to SkScaledCodec

src/codec/SkBmpCodec.cpp

Index: src/codec/SkBmpCodec.cpp
diff --git a/src/codec/SkBmpCodec.cpp b/src/codec/SkBmpCodec.cpp
index 1aa43f583cbcc2a536c6f1b8e8fb6dd15acb7be5..d455db45688fe819deeff2f23b4eb721892d8036 100644
--- a/src/codec/SkBmpCodec.cpp
+++ b/src/codec/SkBmpCodec.cpp
@@ -535,10 +535,18 @@ SkBmpCodec::SkBmpCodec(const SkImageInfo& info, SkStream* stream,
     : INHERITED(info, stream)
     , fBitsPerPixel(bitsPerPixel)
     , fRowOrder(rowOrder)
+    , fSubsetLeft(0)
+    , fSubsetWidth(this->getInfo().width())
 {}
 
 bool SkBmpCodec::onRewind() {
-    return SkBmpCodec::ReadHeader(this->stream(), this->inIco(), nullptr);
+    if (!SkBmpCodec::ReadHeader(this->stream(), this->inIco(), nullptr)) {
+        return false;
+    }
+
+    fSubsetLeft = 0;
+    fSubsetWidth = this->getInfo().width();
+    return true;
 }
 
 int32_t SkBmpCodec::getDstRow(int32_t y, int32_t height) const {
@@ -563,7 +571,8 @@ uint32_t SkBmpCodec::computeNumColors(uint32_t numColors) {
 }
 
 SkCodec::Result SkBmpCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
-        const SkCodec::Options& options, SkPMColor inputColorPtr[], int* inputColorCount) {
+        const SkCodec::Options& options, SkPMColor inputColorPtr[], int* inputColorCount,
+        int subsetLeft, int subsetWidth) {
     if (options.fSubset) {
         // Subsets are not supported.
         return kUnimplemented;
@@ -573,7 +582,9 @@ SkCodec::Result SkBmpCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
         return kInvalidConversion;
     }
 
-    return prepareToDecode(dstInfo, options, inputColorPtr, inputColorCount);
+    this->fSubsetLeft = subsetLeft;
+    this->fSubsetWidth = subsetWidth;
+    return this->prepareToDecode(dstInfo, options, inputColorPtr, inputColorCount);
 }
 
 int SkBmpCodec::onGetScanlines(void* dst, int count, size_t rowBytes) {