Sync-patch with libwebp ver 0.4.1-rc1.

Sync-patch with libwebp ver 0.4.1-rc1 (change#I5346984d2).
  - NEON assembly optimizations:
    - ~25% faster lossy decode / encode (-m 4)
    - ~10% faster lossless decode
    - ~5-10% faster lossless encode (-m 3/4)
  - Arch64 (arm64) & MIPS support/optimizations.

Change-Id: I855b65cec8fad5ec567c276b698e7714dc4bffd2
diff --git a/src/utils/rescaler.h b/src/utils/rescaler.h
index 59b75b4..6699c5b 100644
--- a/src/utils/rescaler.h
+++ b/src/utils/rescaler.h
@@ -52,26 +52,24 @@
 int WebPRescaleNeededLines(const WebPRescaler* const rescaler,
                            int max_num_lines);
 
-// Import a row of data and save its contribution in the rescaler.
-// 'channel' denotes the channel number to be imported.
-void WebPRescalerImportRow(WebPRescaler* const rescaler,
-                           const uint8_t* const src, int channel);
-
 // Import multiple rows over all channels, until at least one row is ready to
 // be exported. Returns the actual number of lines that were imported.
 int WebPRescalerImport(WebPRescaler* const rescaler, int num_rows,
                        const uint8_t* src, int src_stride);
 
+// Import a row of data and save its contribution in the rescaler.
+// 'channel' denotes the channel number to be imported.
+extern void (*WebPRescalerImportRow)(WebPRescaler* const wrk,
+                                     const uint8_t* const src, int channel);
+// Export one row (starting at x_out position) from rescaler.
+extern void (*WebPRescalerExportRow)(WebPRescaler* const wrk, int x_out);
+
 // Return true if there is pending output rows ready.
 static WEBP_INLINE
 int WebPRescalerHasPendingOutput(const WebPRescaler* const rescaler) {
   return (rescaler->y_accum <= 0);
 }
 
-// Export one row from rescaler. Returns the pointer where output was written,
-// or NULL if no row was pending.
-uint8_t* WebPRescalerExportRow(WebPRescaler* const rescaler);
-
 // Export as many rows as possible. Return the numbers of rows written.
 int WebPRescalerExport(WebPRescaler* const rescaler);