Remove base's implicit_cast.

base/macros.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file contains macros and macro-like constructs (e.g., templates) that
 // are commonly used throughout Chromium source. (It may also contain things
 // that are closely related to things that are commonly used that belong in this
 // file.)
 
 #ifndef BASE_MACROS_H_
@@ skipping 37 matching lines @@
 // The expression is a compile-time constant, and therefore can be
 // used in defining new arrays, for example.  If you use arraysize on
 // a pointer by mistake, you will get a compile-time error.
 
 // This template function declaration is used in defining arraysize.
 // Note that the function doesn't need an implementation, as we only
 // use its type.
 template <typename T, size_t N> char (&ArraySizeHelper(T (&array)[N]))[N];
 #define arraysize(array) (sizeof(ArraySizeHelper(array)))
 
-
-// Use implicit_cast as a safe version of static_cast or const_cast
-// for upcasting in the type hierarchy (i.e. casting a pointer to Foo
-// to a pointer to SuperclassOfFoo or casting a pointer to Foo to
-// a const pointer to Foo).
-// When you use implicit_cast, the compiler checks that the cast is safe.
-// Such explicit implicit_casts are necessary in surprisingly many
-// situations where C++ demands an exact type match instead of an
-// argument type convertible to a target type.
-//
-// The From type can be inferred, so the preferred syntax for using
-// implicit_cast is the same as for static_cast etc.:
-//
-//   implicit_cast<ToType>(expr)
-//
-// implicit_cast would have been part of the C++ standard library,
-// but the proposal was submitted too late.  It will probably make
-// its way into the language in the future.
-template<typename To, typename From>
-inline To implicit_cast(From const &f) {
-  return f;
-}
-
 // The COMPILE_ASSERT macro can be used to verify that a compile time
 // expression is true. For example, you could use it to verify the
 // size of a static array:
 //
 //   COMPILE_ASSERT(arraysize(content_type_names) == CONTENT_NUM_TYPES,
 //                  content_type_names_incorrect_size);
 //
 // or to make sure a struct is smaller than a certain size:
 //
 //   COMPILE_ASSERT(sizeof(foo) < 128, foo_too_large);
@@ skipping 98 matching lines @@
 
 // Use these to declare and define a static local variable (static T;) so that
 // it is leaked so that its destructors are not called at exit. If you need
 // thread-safe initialization, use base/lazy_instance.h instead.
 #define CR_DEFINE_STATIC_LOCAL(type, name, arguments) \
   static type& name = *new type arguments
 
 }  // base
 
 #endif  // BASE_MACROS_H_