SkLiteDL: tiny perf tweak

src/core/SkLiteDL.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCanvas.h"
 #include "SkData.h"
 #include "SkImageFilter.h"
@@ skipping 460 matching lines @@
 static void* push(SkTDArray<uint8_t>* bytes, size_t pod, Args&&... args) {
     size_t skip = SkAlignPtr(sizeof(T) + pod);
     auto op = (T*)bytes->append(skip);
     new (op) T{ std::forward<Args>(args)... };
     op->skip = skip;
     return op+1;
 }
 
 template <typename Fn>
 static void map(SkTDArray<uint8_t>* bytes, Fn&& fn) {
-    for (uint8_t* ptr = bytes->begin(); ptr < bytes->end(); ) {
+    auto end = bytes->end();
+    for (uint8_t* ptr = bytes->begin(); ptr < end; ) {
         auto op = (Op*)ptr;
         fn(op);
         ptr += op->skip;
     }
 }
 
 void SkLiteDL::   save() { push   <Save>(&fBytes, 0); }
 void SkLiteDL::restore() { push<Restore>(&fBytes, 0); }
 void SkLiteDL::saveLayer(const SkRect* bounds, const SkPaint* paint,
                          const SkImageFilter* backdrop, SkCanvas::SaveLayerFlags flags) {
@@ skipping 221 matching lines @@
 }
 
 void SkLiteDL::PurgeFreelist() {
     SkAutoMutexAcquire lock(gFreeStackLock);
     while (gFreeStack) {
         SkLiteDL* top = gFreeStack;
         gFreeStack = gFreeStack->fNext;
         delete top;   // Calling unref() here would just put it back on the list!
     }
 }