Make SkSmallAllocator obey the RAII invariants and be expandable

src/core/SkBlitter.cpp

Index: src/core/SkBlitter.cpp
diff --git a/src/core/SkBlitter.cpp b/src/core/SkBlitter.cpp
index b81432533b06966fa27ec83ebf3ed9a254b64cb9..35a213b8b74b30fc1fd0ee953f6bc3c27142212b 100644
--- a/src/core/SkBlitter.cpp
+++ b/src/core/SkBlitter.cpp
@@ -896,14 +896,15 @@ SkBlitter* SkBlitter::Choose(const SkPixmap& device,
         size_t contextSize = shader->contextSize(rec);
         if (contextSize) {
             // Try to create the ShaderContext
-            void* storage = allocator->reserveT<SkShader::Context>(contextSize);
-            shaderContext = shader->createContext(rec, storage);
+            shaderContext = allocator->createWithIniter(
+                contextSize,
+                [&rec, shader](void* storage) {
+                    return shader->createContext(rec, storage);
+                });
             if (!shaderContext) {
-                allocator->freeLast();
                 return allocator->createT<SkNullBlitter>();
             }
             SkASSERT(shaderContext);
-            SkASSERT((void*) shaderContext == storage);
         } else {
             return allocator->createT<SkNullBlitter>();
         }