Revert of Remove old/unused atomicops code

base/base.gypi

Index: base/base.gypi
diff --git a/base/base.gypi b/base/base.gypi
index 0f9196a00c28254e99881cadce88634c73edaafa..ed22cff6c8b950c76e2e9dd76d91d42ae2eece0d 100644
--- a/base/base.gypi
+++ b/base/base.gypi
@@ -91,8 +91,11 @@
           'atomic_ref_count.h',
           'atomic_sequence_num.h',
           'atomicops.h',
+          'atomicops_internals_gcc.h',
           'atomicops_internals_mac.h',
           'atomicops_internals_portable.h',
+          'atomicops_internals_x86_gcc.cc',
+          'atomicops_internals_x86_gcc.h',
           'atomicops_internals_x86_msvc.h',
           'barrier_closure.cc',
           'barrier_closure.h',
@@ -770,6 +773,9 @@
               'sources/': [
                 ['exclude', '^nix/'],
               ],
+              'sources!': [
+                'atomicops_internals_x86_gcc.cc',
+              ],
           }],
           ['<(use_glib)==0 or >(nacl_untrusted_build)==1', {
               'sources!': [
@@ -854,6 +860,7 @@
             ],
             'sources/': [
               # Pull in specific files for host builds.
+              ['include', '^atomicops_internals_x86_gcc\\.cc$'],
               ['include', '^threading/platform_thread_linux\\.cc$'],
             ],
           }],