Add SkCachedData and use it for SkMipMap

This reverts commit 37c5a815d8ea33247968212ef4cc83394ceee1bc.

TBR=mtklein

Review URL: https://codereview.chromium.org/635333002
diff --git a/tests/MipMapTest.cpp b/tests/MipMapTest.cpp
index 33f4672..c8396ef 100644
--- a/tests/MipMapTest.cpp
+++ b/tests/MipMapTest.cpp
@@ -25,7 +25,7 @@
 
     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));