Add gyp files to build NSS in Dart

runtime/tools/gyp/nss_configurations.gypi

+# Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+# for details. 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 is included to modify the configurations to build third-party
+# code from Mozilla's NSS and NSPR libraries, modified by the Chromium project.
+# This code is C code, not C++, and is not warning-free, so we need to remove
+# C++-specific flags, and add flags to supress the warnings in the code.
+# This file is included from gyp files in the runtime/bin/net directory.
+{
+  'variables': {
+    # Used by third_party/nss, which is from Chromium.
+    'os_posix': 1,
+    'os_bsd': 0,
+    'chromeos': 0,
+    'clang': 0,
+  },
+  'target_defaults': {
+    'cflags': [
+      '-Wno-unused-variable',
+      '-Wno-unused-but-set-variable',
+      '-Wno-missing-field-initializers',
+      '-Wno-uninitialized',
+      '-Wno-sign-compare',
+      '-Wno-empty-body',
+      '-Wno-type-limits',
+      '-Wno-pointer-to-int-cast',
+      '-UHAVE_CVAR_BUILT_ON_SEM',
+    ],
+    # Removes these flags from the list cflags.
+    'cflags!': [
+      '-Werror',
+      '-Wall',
+      '-Wvla',
+      '-Woverloaded-virtual',
+      '-ansi',
+      '-fno-exceptions',

[Mads Ager (google), 2012/11/05 12:42:33]

Could you add two sections here? One for disabled warnings and one for flags
that only make sense for C++:

# disable warning flags
'-Werrror',
...
# remove C++ flags
'-fno-exceptions',
...

+      '-fvisibility=hidden',
+      # Not supported for C, only for C++.
+      '-Wnon-virtual-dtor',
+      '-Wno-conversion-null',
+      '-fno-rtti',
+      '-fvisibility-inlines-hidden',
+    ],
+    'configurations': {
+      'Dart_Base': {
+        'xcode_settings': {
+          'WARNING_CFLAGS!': [
+            '-Wall',
+            '-Wextra',
+          ],
+        },
+      },
+      # Dart_Debug and Dart_Release are merged after Dart_Base, so we can
+      # override the 'ansi' and '-Werror' flags set at the global level in
+      # tools/gyp/configurations_xcode.gypi.
+      'Dart_Debug': {
+        'xcode_settings': {
+          # Remove 'ansi' setting.
+          'GCC_C_LANGUAGE_STANDARD': 'c99',
+          'GCC_TREAT_WARNINGS_AS_ERRORS': 'NO', # -Werror off
+        },
+      },
+      'Dart_Release': {
+        'xcode_settings': {
+          # Remove 'ansi' setting.
+          'GCC_C_LANGUAGE_STANDARD': 'c99',
+          'GCC_TREAT_WARNINGS_AS_ERRORS': 'NO', # -Werror off
+        },
+      },
+    },
+  },
+}