Add currScanline() getter to SkCodec API

src/codec/SkCodec_libgif.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_libgif.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 490 matching lines @@
     return get_color_table_fill_value(colorType, colorPtr, fFillIndex);
 }
 
 SkCodec::Result SkGifCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
         const SkCodec::Options& opts, SkPMColor inputColorPtr[], int* inputColorCount) {
     return this->prepareToDecode(dstInfo, inputColorPtr, inputColorCount, this->options());
 }
 
 void SkGifCodec::handleScanlineFrame(int count, int* rowsBeforeFrame, int* rowsInFrame) {
     if (fFrameIsSubset) {
-        const int currRow = this->INHERITED::nextScanline();
+        const int currRow = this->currScanline();
 
         // The number of rows that remain to be skipped before reaching rows that we
         // actually must decode into.
         // This must be at least zero.  We also make sure that it is less than or
         // equal to count, since we will skip at most count rows.
         *rowsBeforeFrame = SkTMin(count, SkTMax(0, fFrameRect.top() - currRow));
 
         // Rows left to decode once we reach the start of the frame.
         const int rowsLeft = count - *rowsBeforeFrame;
 
@@ skipping 60 matching lines @@
 int SkGifCodec::onOutputScanline(int inputScanline) const {
     if (fGif->Image.Interlace) {
         if (inputScanline < fFrameRect.top() || inputScanline >= fFrameRect.bottom()) {
             return inputScanline;
         }
         return get_output_row_interlaced(inputScanline - fFrameRect.top(), fFrameRect.height()) +
                 fFrameRect.top();
     }
     return inputScanline;
 }