Add SkCachedData and use it for SkMipMap

tests/MipMapTest.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 "SkBitmap.h"
 #include "SkMipMap.h"
 #include "SkRandom.h"
 #include "Test.h"
 
 static void make_bitmap(SkBitmap* bm, SkRandom& rand) {
     // for now, Build needs a min size of 2, otherwise it will return NULL.
     // should fix that to support 1 X N, where N > 1 to return non-null.
     int w = 2 + rand.nextU() % 1000;
     int h = 2 + rand.nextU() % 1000;
     bm->allocN32Pixels(w, h);
     bm->eraseColor(SK_ColorWHITE);
 }
 
 DEF_TEST(MipMap, reporter) {
     SkBitmap bm;
     SkRandom rand;
 
     for (int i = 0; i < 500; ++i) {
         make_bitmap(&bm, rand);
-        SkAutoTUnref<SkMipMap> mm(SkMipMap::Build(bm));
+        SkAutoTUnref<SkMipMap> mm(SkMipMap::Build(bm, NULL));
 
         REPORTER_ASSERT(reporter, !mm->extractLevel(SK_Scalar1, NULL));
         REPORTER_ASSERT(reporter, !mm->extractLevel(SK_Scalar1 * 2, NULL));
 
         SkMipMap::Level prevLevel;
         sk_bzero(&prevLevel, sizeof(prevLevel));
 
         SkScalar scale = SK_Scalar1;
         for (int j = 0; j < 30; ++j) {
             scale = scale * 2 / 3;
 
             SkMipMap::Level level;
             if (mm->extractLevel(scale, &level)) {
                 REPORTER_ASSERT(reporter, level.fPixels);
                 REPORTER_ASSERT(reporter, level.fWidth > 0);
                 REPORTER_ASSERT(reporter, level.fHeight > 0);
                 REPORTER_ASSERT(reporter, level.fRowBytes >= level.fWidth * 4);
 
                 if (prevLevel.fPixels) {
                     REPORTER_ASSERT(reporter, level.fWidth <= prevLevel.fWidth);
                     REPORTER_ASSERT(reporter, level.fHeight <= prevLevel.fHeight);
                 }
                 prevLevel = level;
             }
         }
     }
 }