Move headers used by headers in include/ to include/private.

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
 
@@ skipping 55 matching lines @@
         R call(Args... args) const override { return fFn(Forward(args)...); }
         Interface* clone() const { return SkNEW_ARGS(FnPtrImpl, (fFn)); }
     private:
         R (*fFn)(Args...);
     };
 
     SkAutoTDelete<Interface> fFunction;
 };
 
 #endif//SkFunction_DEFINED