Make SkSmallAllocator obey the RAII invariants and be expandable

src/core/SkDrawLooper.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDrawLooper.h"
 #include "SkCanvas.h"
 #include "SkMatrix.h"
 #include "SkPaint.h"
 #include "SkRect.h"
 #include "SkSmallAllocator.h"
 
 bool SkDrawLooper::canComputeFastBounds(const SkPaint& paint) const {
     SkCanvas canvas;
     SkSmallAllocator<1, 32> allocator;
-    void* buffer = allocator.reserveT<SkDrawLooper::Context>(this->contextSize());
 
-    SkDrawLooper::Context* context = this->createContext(&canvas, buffer);
+    SkDrawLooper::Context* context = allocator.createWithIniter(
+        this->contextSize(),
+        [&](void* buffer) {
+            return this->createContext(&canvas, buffer);
+        });
     for (;;) {
         SkPaint p(paint);
         if (context->next(&canvas, &p)) {
             p.setLooper(nullptr);
             if (!p.canComputeFastBounds()) {
                 return false;
             }
         } else {
             break;
         }
     }
     return true;
 }
 
 void SkDrawLooper::computeFastBounds(const SkPaint& paint, const SkRect& s,
                                      SkRect* dst) const {
     // src and dst rects may alias and we need to keep the original src, so copy it.
     const SkRect src = s;
 
     SkCanvas canvas;
     SkSmallAllocator<1, 32> allocator;
-    void* buffer = allocator.reserveT<SkDrawLooper::Context>(this->contextSize());
 
     *dst = src;   // catch case where there are no loops
-    SkDrawLooper::Context* context = this->createContext(&canvas, buffer);
+    SkDrawLooper::Context* context = allocator.createWithIniter(
+        this->contextSize(),
+        [&](void* buffer) {
+            return this->createContext(&canvas, buffer);
+        });
     for (bool firstTime = true;; firstTime = false) {
         SkPaint p(paint);
         if (context->next(&canvas, &p)) {
             SkRect r(src);
 
             p.setLooper(nullptr);
             p.computeFastBounds(r, &r);
             canvas.getTotalMatrix().mapRect(&r);
 
             if (firstTime) {
                 *dst = r;
             } else {
                 dst->join(r);
             }
         } else {
             break;
         }
     }
 }
 
 bool SkDrawLooper::asABlurShadow(BlurShadowRec*) const {
     return false;
 }