Put irt and untrusted TC dependencies behind a flag.

build/common.gypi

 # 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 605 matching lines @@
 
     # The Java Bridge is not compiled in by default.
     'java_bridge%': 0,
 
     # TODO(dpranke): This determines whether we should attempt to build DRT
     # et al. from WebKit/Source/WebKit.gyp or Tools/Tools.gyp. This
     # flag should only be needed temporarily. See
     # https://bugs.webkit.org/show_bug.cgi?id=68463.
     'build_webkit_exes_from_webkit_gyp%': 1,
 
+    # This flag is only used when disable_nacl==0 and disables all those
+    # subcomponents which would require the installation of a native_client
+    # untrusted toolchain.
+    'disable_nacl_untrusted%': 0,
+
     'conditions': [
       # Used to disable Native Client at compile time, for platforms where it
       # isn't supported (ARM)
-      ['target_arch=="arm"', {
+      ['target_arch=="arm" and chromeos == 1', {
         'disable_nacl%': 1,
        }, {
         'disable_nacl%': 0,
       }],
       ['os_posix==1 and OS!="mac" and OS!="android"', {
         # This will set gcc_version to XY if you are running gcc X.Y.*.
         # This is used to tweak build flags for gcc 4.4.
         'gcc_version%': '<!(python <(DEPTH)/build/compiler_version.py)',
         # Figure out the python architecture to decide if we build pyauto.
         'python_arch%': '<!(<(DEPTH)/build/linux/python_arch.sh <(sysroot)/usr/<(system_libdir)/libpython<(python_ver).so.1.0)',
@@ skipping 2026 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }