Add subsetting to SkScanlineDecoder

src/codec/SkWebpCodec.cpp

Index: src/codec/SkWebpCodec.cpp
diff --git a/src/codec/SkWebpCodec.cpp b/src/codec/SkWebpCodec.cpp
index a0fab0a153d67f0d32375ac7405d06314a7bb317..c5f37d21dae15bf808f969be2b0f1101384a4765 100644
--- a/src/codec/SkWebpCodec.cpp
+++ b/src/codec/SkWebpCodec.cpp
@@ -140,15 +140,6 @@ static WEBP_CSP_MODE webp_decode_mode(SkColorType ct, bool premultiply) {
 static const size_t BUFFER_SIZE = 4096;
 
 bool SkWebpCodec::onGetValidSubset(SkIRect* desiredSubset) const {
-    if (!desiredSubset) {
-        return false;
-    }
-
-    SkIRect bounds = SkIRect::MakeSize(this->getInfo().dimensions());
-    if (!desiredSubset->intersect(bounds)) {
-        return false;
-    }
-
     // As stated below, libwebp snaps to even left and top. Make sure top and left are even, so we
     // decode this exact subset.
     // Leave right and bottom unmodified, so we suggest a slightly larger subset than requested.