SkAdvancedTypefaceMetrics: improve robustness

src/pdf/SkSinglyLinkedList.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef SkSinglyLinkedList_DEFINED
 #define SkSinglyLinkedList_DEFINED
 
 #include <utility>
 
 #include "SkTypes.h"
 
 template <typename T> class SkSinglyLinkedList {
     struct Node;
 public:
     SkSinglyLinkedList() : fHead(nullptr), fTail(nullptr) {}
     ~SkSinglyLinkedList() { this->reset(); }
     void reset() {
         SkASSERT(fHead != nullptr || nullptr == fTail);
+        // Use a while loop rather than recursion to avoid stack overflow.
         Node* node = fHead;
         while (node) {
             Node* next = node->fNext;
             SkASSERT(next != nullptr || node == fTail);
             delete node;
             node = next;
         }
         fHead = nullptr;
         fTail = nullptr;
     }
@@ skipping 55 matching lines @@
         Node* fNext;
         template <class... Args>
         Node(Args&&... args) : fData(std::forward<Args>(args)...), fNext(nullptr) {}
     };
     Node* fHead;
     Node* fTail;
     SkSinglyLinkedList(const SkSinglyLinkedList<T>&) = delete;
     SkSinglyLinkedList& operator=(const SkSinglyLinkedList<T>&) = delete;
 };
 #endif  // SkSinglyLinkedList_DEFINED