[KeyboardLock] Adding a SystemKeyboardLock feature

This feature controls whether the low-level keyboard hook is enabled
when keyboard lock is requested.  I wanted to separate browser and
system level keyboard lock functionality as I get closer to launching
the blink api for keyboard lock.  This will allow us to release
browser-level keyboard lock w/o the system hooks if needed and will
also give us the ability to target a finch kill switch for the
system-level functionality if needed.

BUG=680809

Change-Id: I2d522046c90fd8776bfb1d9c53978f2c41e1c7cc
Reviewed-on: https://chromium-review.googlesource.com/1046154
Reviewed-by: Scott Violet <[email protected]>
Commit-Queue: Joe Downing <[email protected]>
Cr-Commit-Position: refs/heads/master@{#558367}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 2906b88..367644d 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2255,6 +2255,9 @@
     {"keyboard-lock-api", flag_descriptions::kKeyboardLockApiName,
      flag_descriptions::kKeyboardLockApiDescription, kOsDesktop,
      FEATURE_VALUE_TYPE(features::kKeyboardLockAPI)},
+    {"system-keyboard-lock", flag_descriptions::kSystemKeyboardLockName,
+     flag_descriptions::kSystemKeyboardLockDescription, kOsDesktop,
+     FEATURE_VALUE_TYPE(features::kSystemKeyboardLock)},
     {"experimental-keyboard-lock-ui",
      flag_descriptions::kExperimentalKeyboardLockUiName,
      flag_descriptions::kExperimentalKeyboardLockUiDescription, kOsDesktop,