Add scanline decoding to SkCodec.

src/codec/SkCodec.cpp

Index: src/codec/SkCodec.cpp
diff --git a/src/codec/SkCodec.cpp b/src/codec/SkCodec.cpp
index 12341f59295fcec7e16c6fab0eea93f8cd78dba0..8f67a1b5a64ba9e7d7434a55496ecd180e9ebcbc 100644
--- a/src/codec/SkCodec.cpp
+++ b/src/codec/SkCodec.cpp
@@ -59,3 +59,12 @@ bool SkCodec::rewindIfNeeded() {
     fNeedsRewind = true;
     return !neededRewind || fStream->rewind();
 }
+
+SkScanlineDecoder* SkCodec::getScanlineDecoder(const SkImageInfo& dstInfo) {
+    fScanlineDecoder.reset(NULL);
+    if (!rewindIfNeeded()) {
+        return NULL;
+    }
+    fScanlineDecoder.reset(this->onGetScanlineDecoder(dstInfo));
+    return fScanlineDecoder.get();
+}