Replace SkFunction with std::function

include/private/SkFunction.h

-/*
- * Copyright 2015 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#ifndef SkFunction_DEFINED
-#define SkFunction_DEFINED
-
-// TODO: document, more pervasive move support in constructors, small-Fn optimization
-
-#include "SkUtility.h"
-#include "SkUniquePtr.h"
-#include "SkTypes.h"
-
-template <typename> class SkFunction;
-
-template <typename R, typename... Args>
-class SkFunction<R(Args...)> {
-public:
-    SkFunction() {}
-
-    template <typename Fn>
-    SkFunction(const Fn& fn)
-        : fFunction(new LambdaImpl<Fn>(fn)) {}
-
-    SkFunction(R (*fn)(Args...)) : fFunction(new FnPtrImpl(fn)) {}
-
-    SkFunction(const SkFunction& other) { *this = other; }
-    SkFunction& operator=(const SkFunction& other) {
-        if (this != &other) {
-            fFunction.reset(other.fFunction.get() ? other.fFunction->clone() : nullptr);
-        }
-        return *this;
-    }
-
-    R operator()(Args... args) const {
-        SkASSERT(fFunction.get());
-        return fFunction->call(skstd::forward<Args>(args)...);
-    }
-
-private:
-    struct Interface {
-        virtual ~Interface() {}
-        virtual R call(Args...) const = 0;
-        virtual Interface* clone() const = 0;
-    };
-
-    template <typename Fn>
-    class LambdaImpl final : public Interface {
-    public:
-        LambdaImpl(const Fn& fn) : fFn(fn) {}
-
-        R call(Args... args) const override { return fFn(skstd::forward<Args>(args)...); }
-        Interface* clone() const override { return new LambdaImpl<Fn>(fFn); }
-
-    private:
-        Fn fFn;
-    };
-
-    class FnPtrImpl final : public Interface {
-    public:
-        FnPtrImpl(R (*fn)(Args...)) : fFn(fn) {}
-
-        R call(Args... args) const override { return fFn(skstd::forward<Args>(args)...); }
-        Interface* clone() const override { return new FnPtrImpl(fFn); }
-
-    private:
-        R (*fFn)(Args...);
-    };
-
-    skstd::unique_ptr<Interface> fFunction;
-};
-
-#endif//SkFunction_DEFINED