Rearrange SkRecord with small N in mind

src/core/SkVarAlloc.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
 #include "SkVarAlloc.h"
 
 // We use non-standard malloc diagnostic methods to make sure our allocations are sized well.
 #if defined(SK_BUILD_FOR_MAC)
     #include <malloc/malloc.h>
 #elif defined(SK_BUILD_FOR_UNIX) || defined(SK_BUILD_FOR_WIN32)
     #include <malloc.h>
 #endif
 
 struct SkVarAlloc::Block {
     Block* prev;
     char* data() { return (char*)(this + 1); }
 
     static Block* Alloc(Block* prev, size_t size, unsigned flags) {
         SkASSERT(size >= sizeof(Block));
         Block* b = (Block*)sk_malloc_flags(size, flags);
         b->prev = prev;
         return b;
     }
 };
 
 SkVarAlloc::SkVarAlloc(size_t minLgSize)
     : fByte(NULL)
     , fRemaining(0)
     , fLgSize(minLgSize)
     , fBlock(NULL) {}
 
+SkVarAlloc::SkVarAlloc(size_t minLgSize, char* storage, size_t len)
+    : fByte(storage)
+    , fRemaining(len)
+    , fLgSize(minLgSize)
+    , fBlock(NULL) {}
+
 SkVarAlloc::~SkVarAlloc() {
     Block* b = fBlock;
     while (b) {
         Block* prev = b->prev;
         sk_free(b);
         b = prev;
     }
 }
 
 void SkVarAlloc::makeSpace(size_t bytes, unsigned flags) {
@@ skipping 27 matching lines @@
 #endif
 }
 
 size_t SkVarAlloc::approxBytesAllocated() const {
     size_t sum = 0;
     for (Block* b = fBlock; b; b = b->prev) {
         sum += heap_size(b);
     }
     return sum;
 }