Add about:flags entry for Mac V2 sandbox.

chrome/browser/flag_descriptions.cc

Index: chrome/browser/flag_descriptions.cc
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index e88f4d37d1bb8fc0b5e135f415b59f574afb23c7..bb6c581d30b44723047f5618fae8ff2a8e1c644b 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -1472,6 +1472,12 @@ const char kAppInfoDialogDescription[] =
     "permissions dialog, or the details link (which is a link to the Web "
     "Store).";
 
+const char kMacV2SandboxName[] = "Mac V2 Sandbox";
+
+const char kMacV2SandboxDescription[] =
+    "Eliminates the unsandboxed warmup phase and sandboxes processes for their "
+    "entire life cycle.";
+
 const char kMacViewsNativeAppWindowsName[] = "Toolkit-Views App Windows.";
 
 const char kMacViewsNativeAppWindowsDescription[] =