Linux: add support for SELinux.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index aeb5d111ad29c2c80c2ecbca02f465b27c77a462..7b8ad12f20cd1233186115bc0af796298cde837a 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -112,6 +112,9 @@
     # sandbox the zygote process and, thus, all renderer processes.
     'linux_sandbox_path%': '',
 
+    # Set this to true to enable SELinux support.
+    'selinux%': 0,
+
     'conditions': [
       ['OS=="linux"', {
         'conditions': [
@@ -189,6 +192,9 @@
       ['chromeos==1', {
         'defines': ['OS_CHROMEOS=1'],
       }],
+      ['selinux==1', {
+        'defines': ['CHROMIUM_SELINUX=1'],
+      }],
       ['coverage!=0', {
         'conditions': [
           ['OS=="mac"', {