Revert of remove Sk64 from public API, and start to remove usage internally

src/images/SkImageDecoder_libwebp.cpp

 /*
  * Copyright 2010, The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
@@ skipping 62 matching lines @@
     VP8StatusCode status = WebPGetFeatures(buffer, totalBytesRead, &features);
     if (VP8_STATUS_OK != status) {
         return false; // Invalid WebP file.
     }
     *width = features.width;
     *height = features.height;
     *alpha = features.has_alpha;
 
     // sanity check for image size that's about to be decoded.
     {
-        int64_t size = sk_64_mul(*width, *height);
-        if (!sk_64_isS32(size)) {
+        Sk64 size;
+        size.setMul(*width, *height);
+        if (size.isNeg() || !size.is32()) {
             return false;
         }
         // now check that if we are 4-bytes per pixel, we also don't overflow
-        if (sk_64_asS32(size) > (0x7FFFFFFF >> 2)) {
+        if (size.get32() > (0x7FFFFFFF >> 2)) {
             return false;
         }
     }
     return true;
 }
 
 class SkWEBPImageDecoder: public SkImageDecoder {
 public:
     SkWEBPImageDecoder() {
         fInputStream = NULL;
@@ skipping 496 matching lines @@
     return SkImageDecoder::kUnknown_Format;
 }
 
 static SkImageEncoder* sk_libwebp_efactory(SkImageEncoder::Type t) {
       return (SkImageEncoder::kWEBP_Type == t) ? SkNEW(SkWEBPImageEncoder) : NULL;
 }
 
 static SkImageDecoder_DecodeReg gDReg(sk_libwebp_dfactory);
 static SkImageDecoder_FormatReg gFormatReg(get_format_webp);
 static SkImageEncoder_EncodeReg gEReg(sk_libwebp_efactory);