Track the active ExtensionKeybindingRegistry and make it available to EventRewriter.

chrome/browser/ui/cocoa/browser_window_cocoa.mm

Index: chrome/browser/ui/cocoa/browser_window_cocoa.mm
diff --git a/chrome/browser/ui/cocoa/browser_window_cocoa.mm b/chrome/browser/ui/cocoa/browser_window_cocoa.mm
index de98e9b404c23389c2f9ba155643707f5db0cfc4..3c2cc7f28b22cbf94b1c2cc6224f32f4ebd61e4b 100644
--- a/chrome/browser/ui/cocoa/browser_window_cocoa.mm
+++ b/chrome/browser/ui/cocoa/browser_window_cocoa.mm
@@ -56,6 +56,7 @@
 #include "content/public/browser/notification_details.h"
 #include "content/public/browser/notification_source.h"
 #include "content/public/browser/web_contents.h"
+#include "ui/base/accelerators/accelerator.h"
 #include "ui/base/l10n/l10n_util_mac.h"
 #include "ui/gfx/rect.h"
 
@@ -726,3 +727,9 @@ void BrowserWindowCocoa::ExecuteExtensionCommand(
     const extensions::Command& command) {
   [cocoa_controller() executeExtensionCommand:extension->id() command:command];
 }
+
+bool BrowserWindowCocoa::IsExtensionCommandRegistered(
+    const ui::Accelerator& accelerator) {
+  return [cocoa_controller()
+      isExtensionCommandRegisteredForAccelerator:accelerator];
+}