Update sandbox/linux/ from https://crrev.com/344610

Pull sandbox changes from upstream, up to
https://crrev.com/344610

This mostly include fixes and cleanups, including for a complex TLS
corruption issue fixed in crbug.com/512623

This required a minimal workaround to work with the older
version of base/ of Mojo.

R=jamesr@chromium.org, mdempsky@chromium.org

Review URL: https://codereview.chromium.org/1310773006 .
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 7b3b26c..a7c70c4 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -165,6 +165,7 @@
     'OS_LINUX',
     'OS_MACOSX',
     'OS_NACL',
+    'OS_NACL_NONSFI',
     'OS_OPENBSD',
     'OS_POSIX',
     'OS_QNX',