Add information on the requirements for a new Chromium port.

build/build_config.h

 // Copyright (c) 2012 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 adds defines about the platform we're currently building on.
 //  Operating System:
 //    OS_WIN / OS_MACOSX / OS_LINUX / OS_POSIX (MACOSX or LINUX) /
 //    OS_NACL (NACL_SFI or NACL_NONSFI) / OS_NACL_SFI / OS_NACL_NONSFI
 //    OS_CHROMEOS is set by the build system
 //  Compiler:
@@ skipping 48 matching lines @@
 #define OS_OPENBSD 1
 #elif defined(__sun)
 #define OS_SOLARIS 1
 #elif defined(__QNXNTO__)
 #define OS_QNX 1
 #elif defined(_AIX)
 #define OS_AIX 1
 #else
 #error Please add support for your platform in build/build_config.h
 #endif
+// NOTE: Adding a new port? Please follow
+// https://chromium.googlesource.com/chromium/src/+/master/docs/new_port_policy.md
 
 #if defined(USE_OPENSSL_CERTS) && defined(USE_NSS_CERTS)
 #error Cannot use both OpenSSL and NSS for certificates
 #endif
 
 // For access to standard BSD features, use OS_BSD instead of a
 // more specific macro.
 #if defined(OS_FREEBSD) || defined(OS_NETBSD) || defined(OS_OPENBSD)
 #define OS_BSD 1
 #endif
@@ skipping 105 matching lines @@
 #if defined(OS_ANDROID)
 // The compiler thinks std::string::const_iterator and "const char*" are
 // equivalent types.
 #define STD_STRING_ITERATOR_IS_CHAR_POINTER
 // The compiler thinks base::string16::const_iterator and "char16*" are
 // equivalent types.
 #define BASE_STRING16_ITERATOR_IS_CHAR16_POINTER
 #endif
 
 #endif  // BUILD_BUILD_CONFIG_H_