Add currScanline() getter to SkCodec API

src/codec/SkCodec_libpng.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCodec_libpng.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 750 matching lines @@
             // decoding is the exception, since it needs to rewind between
             // calls to getScanlines. Keep track of fCurrScanline, to undo the
             // reset.
             const int currScanline = this->nextScanline();
             // This method would never be called if currScanline is -1
             SkASSERT(currScanline != -1);
 
             if (!this->rewindIfNeeded()) {
                 return kCouldNotRewind;
             }
-            this->updateNextScanline(currScanline);
+            this->updateCurrScanline(currScanline);
         }
 
         if (setjmp(png_jmpbuf(this->png_ptr()))) {
             SkCodecPrintf("setjmp long jump!\n");
             // FIXME (msarett): Returning 0 is pessimistic.  If we can complete a single pass,
             // we may be able to report that all of the memory has been initialized.  Even if we
             // fail on the first pass, we can still report than some scanlines are initialized.
             return 0;
         }
         SkAutoMalloc storage(count * fSrcRowBytes);
@@ skipping 84 matching lines @@
     }
 
     if (1 == numberPasses) {
         return new SkPngScanlineDecoder(imageInfo, streamDeleter.detach(), chunkReader,
                                         png_ptr, info_ptr, bitDepth);
     }
 
     return new SkPngInterlacedScanlineDecoder(imageInfo, streamDeleter.detach(), chunkReader,
                                               png_ptr, info_ptr, bitDepth, numberPasses);
 }