Add currScanline() getter to SkCodec API

include/codec/SkCodec.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkCodec_DEFINED
 #define SkCodec_DEFINED
 
@@ skipping 379 matching lines @@
      *  decoder.
      *
      *  This will equal fCurrScanline, except in the case of strangely
      *  encoded image types (bottom-up bmps, interlaced gifs).
      *
      *  Results are undefined when not in scanline decoding mode.
      */
     int nextScanline() const { return this->outputScanline(fCurrScanline); }
 
     /**
-     * Returns the output y-coordinate of the row that corresponds to an input
-     * y-coordinate.  The input y-coordinate represents where the scanline
-     * is located in the encoded data.
+     *  Returns the output y-coordinate of the row that corresponds to an input
+     *  y-coordinate.  The input y-coordinate represents where the scanline
+     *  is located in the encoded data.
      *
      *  This will equal inputScanline, except in the case of strangely
      *  encoded image types (bottom-up bmps, interlaced gifs).
      */
     int outputScanline(int inputScanline) const;
 
 protected:
     SkCodec(const SkImageInfo&, SkStream*);
 
     virtual SkISize onGetScaledDimensions(float /* desiredScale */) const {
@@ skipping 91 matching lines @@
     /**
      *  The remaining functions revolve around decoding scanlines.
      */
 
     /**
      *  Most images types will be kTopDown and will not need to override this function.
      */
     virtual SkScanlineOrder onGetScanlineOrder() const { return kTopDown_SkScanlineOrder; }
 
     /**
-     *  Update the next scanline. Used by interlaced png.
+     *  Update the current scanline. Used by interlaced png.
      */
-    void updateNextScanline(int newY) { fCurrScanline = newY; }
+    void updateCurrScanline(int newY) { fCurrScanline = newY; }
 
     const SkImageInfo& dstInfo() const { return fDstInfo; }
 
     const SkCodec::Options& options() const { return fOptions; }
 
+    /**
+     *  Returns the number of scanlines that have been decoded so far.
+     *  This is unaffected by the SkScanlineOrder.
+     *
+     *  Returns -1 if we have not started a scanline decode.
+     */
+    int currScanline() const { return fCurrScanline; }
+
     virtual int onOutputScanline(int inputScanline) const;
 
 private:
     const SkImageInfo       fSrcInfo;
     SkAutoTDelete<SkStream> fStream;
     bool                    fNeedsRewind;
     // These fields are only meaningful during scanline decodes.
     SkImageInfo             fDstInfo;
     SkCodec::Options        fOptions;
     int                     fCurrScanline;
@@ skipping 55 matching lines @@
      *  May create a sampler, if one is not currently being used. Otherwise, does
      *  not affect ownership.
      *
      *  Only valid during scanline decoding.
      */
     virtual SkSampler* getSampler(bool /*createIfNecessary*/) { return nullptr; }
 
     friend class SkSampledCodec;
 };
 #endif // SkCodec_DEFINED