Rearrange SkRecord with small N in mind

src/core/SkVarAlloc.h

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
 #ifndef SkVarAlloc_DEFINED
 #define SkVarAlloc_DEFINED
 
 #include "SkTypes.h"
 
 class SkVarAlloc : SkNoncopyable {
 public:
     // Smallest block we'll allocate is 2**N bytes.
     explicit SkVarAlloc(size_t minLgSize);
+    // Same as above, but first uses up to len bytes from storage.
+    SkVarAlloc(size_t minLgSize, char* storage, size_t len);
+
     ~SkVarAlloc();
 
     // Returns contiguous bytes aligned at least for pointers.  You may pass SK_MALLOC_THROW, etc.
     char* alloc(size_t bytes, unsigned sk_malloc_flags) {
         bytes = SkAlignPtr(bytes);
 
         if (bytes > fRemaining) {
             this->makeSpace(bytes, sk_malloc_flags);
         }
         SkASSERT(bytes <= fRemaining);
@@ skipping 14 matching lines @@
     char* fByte;
     unsigned fRemaining;
     unsigned fLgSize;
 
     struct Block;
     Block* fBlock;
 };
 SK_COMPILE_ASSERT(sizeof(SkVarAlloc) <= 24, SkVarAllocSize);
 
 #endif//SkVarAlloc_DEFINED