Make use_nss a gyp var so that aura can build w/ nss.

build/build_config.h

 // Copyright (c) 2011 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)
 //  Compiler:
 //    COMPILER_MSVC / COMPILER_GCC
 //  Processor:
@@ skipping 26 matching lines @@
 #define OS_OPENBSD 1
 #define TOOLKIT_GTK
 #elif defined(__sun)
 #define OS_SOLARIS 1
 #define TOOLKIT_GTK
 #else
 #error Please add support for your platform in build/build_config.h
 #endif
 
 #if defined(OS_LINUX) || defined(OS_FREEBSD) || defined(OS_OPENBSD) || \
-    defined(OS_SOLARIS) || defined(OS_ANDROID)
-#if !defined(USE_OPENSSL)
-#define USE_NSS 1  // Default to use NSS for crypto, unless OpenSSL is chosen.
-#endif
-#ifndef OS_ANDROID
+    defined(OS_SOLARIS)
 #define USE_X11 1  // Use X for graphics.
 #endif
-#endif
 
 #if defined(USE_OPENSSL) && defined(USE_NSS)
 #error Cannot use both OpenSSL and NSS
 #endif
 
 // For access to standard POSIXish features, use OS_POSIX instead of a
 // more specific macro.
 #if defined(OS_MACOSX) || defined(OS_LINUX) || defined(OS_FREEBSD) ||     \
     defined(OS_OPENBSD) || defined(OS_SOLARIS) || defined(OS_ANDROID) ||  \
     defined(OS_NACL)
@@ skipping 73 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_