Make SkSmallAllocator obey the RAII invariants and be expandable

src/core/SkDrawLooper.cpp

Index: src/core/SkDrawLooper.cpp
diff --git a/src/core/SkDrawLooper.cpp b/src/core/SkDrawLooper.cpp
index aa53f2e3a13176893d84fabaaec25848bd93b288..e372e8f157f3214960bcb7e16a549c7d56e8135a 100644
--- a/src/core/SkDrawLooper.cpp
+++ b/src/core/SkDrawLooper.cpp
@@ -15,9 +15,12 @@
 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)) {
@@ -39,10 +42,13 @@ void SkDrawLooper::computeFastBounds(const SkPaint& paint, const SkRect& 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)) {