cocoa: add experimental tabstrip keyboard focus support

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 5b0ceda3f8b4a3876502a7f790237e24162884b1..77a675b984ad17391f5ae941b78f298c10fb62e4 100644
--- a/chrome/common/chrome_features.cc
+++ b/chrome/common/chrome_features.cc
@@ -74,6 +74,10 @@ const base::Feature kBrowserHangFixesExperiment{
 // Enables or disables the browser's touch bar.
 const base::Feature kBrowserTouchBar{"BrowserTouchBar",
                                      base::FEATURE_ENABLED_BY_DEFAULT};
+
+// Enables or disables keyboard focus for the tab strip.
+const base::Feature kTabStripKeyboardFocus{"TabStripKeyboardFocus",
+                                           base::FEATURE_DISABLED_BY_DEFAULT};
 #endif  // defined(OS_MACOSX)
 
 #if defined(OS_ANDROID)