Linux: add a Credentials class to handle Linux capabilities.

sandbox/linux/sandbox_linux.gypi

Index: sandbox/linux/sandbox_linux.gypi
diff --git a/sandbox/linux/sandbox_linux.gypi b/sandbox/linux/sandbox_linux.gypi
index 29639f8f648524e477aa0d5a10d113a26fc5655f..3b2df8b118b560466fd39387b70a0297ce416295 100644
--- a/sandbox/linux/sandbox_linux.gypi
+++ b/sandbox/linux/sandbox_linux.gypi
@@ -7,8 +7,10 @@
     'conditions': [
       ['OS=="linux"', {
         'compile_suid_client': 1,
+        'compile_credentials': 1,
       }, {
         'compile_suid_client': 0,
+        'compile_credentials': 0,
       }],
       ['((OS=="linux" or OS=="android") and '
              '(target_arch=="ia32" or target_arch=="x64" or '
@@ -149,6 +151,18 @@
       'dependencies': [
         '../base/base.gyp:base',
       ],
+      'conditions': [
+        ['compile_credentials==1', {
+          'sources': [
+            'services/credentials.cc',
+            'services/credentials.h',
+          ],
+          'dependencies': [
+            # for capabilities.cc.
+            '../build/linux/system.gyp:libcap',
+          ],
+        }],
+      ],
       'include_dirs': [
         '..',
       ],