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 cd4dcbc2a509349838e5957b76f4535f00083c0c..980a5e447b13c416add858516fef6113be115a94 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -495,9 +495,11 @@ public:
         }
 
         if (SkDrawLooper* looper = paint.getLooper()) {
-            void* buffer = fLooperContextAllocator.reserveT<SkDrawLooper::Context>(
-                    looper->contextSize());
-            fLooperContext = looper->createContext(canvas, buffer);
+            fLooperContext = fLooperContextAllocator.createWithIniterT<SkDrawLooper::Context>(
+                looper->contextSize(),
+                [&](void* buffer) {
+                    return looper->createContext(canvas, buffer);
+                });
             fIsSimple = false;
         } else {
             fLooperContext = nullptr;