Remove base's implicit_cast.

base/macros.h

Index: base/macros.h
diff --git a/base/macros.h b/base/macros.h
index 53b3926cd2424ac355304f1110e0150696aec4ce..c5f503fbc3ae9158f82ecd3f487ac0e13bb7ae77 100644
--- a/base/macros.h
+++ b/base/macros.h
@@ -55,29 +55,6 @@
 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: