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

src/core/SkMipMap.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkMipMap.h"
 #include "SkBitmap.h"
 #include "SkColorPriv.h"
@@ skipping 91 matching lines @@
     }
     c += expand4444(*p);
     if (x < src.width() - 1) {
         p += 1;
     }
     c += expand4444(*p);
 
     *dst->getAddr16(x >> 1, y >> 1) = (uint16_t)collaps4444(c >> 2);
 }
 
+static bool isPos32Bits(const Sk64& value) {
+    return !value.isNeg() && value.is32();
+}
+
 SkMipMap::Level* SkMipMap::AllocLevels(int levelCount, size_t pixelSize) {
     if (levelCount < 0) {
         return NULL;
     }
-    int64_t size = sk_64_mul(levelCount + 1, sizeof(Level)) + pixelSize;
-    if (!sk_64_isS32(size)) {
+    Sk64 size;
+    size.setMul(levelCount + 1, sizeof(Level));
+    size.add(SkToS32(pixelSize));
+    if (!isPos32Bits(size)) {
         return NULL;
     }
-    return (Level*)sk_malloc_throw(sk_64_asS32(size));
+    return (Level*)sk_malloc_throw(size.get32());
 }
 
 SkMipMap* SkMipMap::Build(const SkBitmap& src) {
     void (*proc)(SkBitmap* dst, int x, int y, const SkBitmap& src);
 
     const SkBitmap::Config config = src.config();
     switch (config) {
         case SkBitmap::kARGB_8888_Config:
             proc = downsampleby2_proc32;
             break;
@@ skipping 116 matching lines @@
     }
 
     if (level > fCount) {
         level = fCount;
     }
     if (levelPtr) {
         *levelPtr = fLevels[level - 1];
     }
     return true;
 }