Add an experimental keyboard lock, where Esc must be held to exit.

chrome/common/chrome_features.cc

Index: chrome/common/chrome_features.cc
diff --git a/chrome/common/chrome_features.cc b/chrome/common/chrome_features.cc
index a3787180e8e2a569460279a09df2c2b9ce9831c6..1737bea0bf72dd87ae46e0dd0a5fa0e2e3b3658c 100644
--- a/chrome/common/chrome_features.cc
+++ b/chrome/common/chrome_features.cc
@@ -14,6 +14,11 @@ const base::Feature kAutomaticTabDiscarding{"AutomaticTabDiscarding",
                                             base::FEATURE_DISABLED_BY_DEFAULT};
 #endif  // defined(OS_WIN) || defined(OS_MACOSX)
 
+// An experimental fullscreen prototype that allows pages to map browser and
+// system-reserved keyboard shortcuts.
+const base::Feature kExperimentalKeyboardLockUI{
+    "ExperimentalKeyboardLockUI", base::FEATURE_DISABLED_BY_DEFAULT};
+
 #if defined(GOOGLE_CHROME_BUILD) && defined(OS_LINUX) && !defined(OS_CHROMEOS)
 // Enables showing the "This computer will no longer receive Google Chrome
 // updates" infobar instead of the "will soon stop receiving" infobar on