Make SkSmallAllocator obey the RAII invariants and be expandable

src/core/SkCanvas.cpp

Index: src/core/SkCanvas.cpp
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index a8d73a982a5f591f116b3189d78fa64a5cb60860..eddf106ae4a405c1a18c1456109062efd9ed0d74 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -496,9 +496,11 @@ public:
         }
 
         if (SkDrawLooper* looper = paint.getLooper()) {
-            void* buffer = fLooperContextAllocator.reserveT<SkDrawLooper::Context>(
-                    looper->contextSize());
-            fLooperContext = looper->createContext(canvas, buffer);
+            fLooperContext = fLooperContextAllocator.createWithIniter(
+                looper->contextSize(),
+                [&](void* buffer) {
+                    return looper->createContext(canvas, buffer);
+                });
             fIsSimple = false;
         } else {
             fLooperContext = nullptr;