Show a warning bubble when the IME extension is activated.

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 de9dce3aa95e676af9dfce08049c7b974cf6c6e9..1918a850d17de90c5a7f6ab0bfae2787be88ee71 100644
--- a/chrome/browser/ui/cocoa/browser_window_cocoa.mm
+++ b/chrome/browser/ui/cocoa/browser_window_cocoa.mm
@@ -850,3 +850,10 @@ void BrowserWindowCocoa::ExecuteExtensionCommand(
 ExclusiveAccessContext* BrowserWindowCocoa::GetExclusiveAccessContext() {
   return [controller_ exclusiveAccessController];
 }
+
+void BrowserWindowCocoa::ShowImeWarningBubble(
+    const extensions::Extension* extension,
+    const base::Callback<void(ImeWarningBubblePermissionStatus status)>&
+        callback) {
+  NOTREACHED() << "The IME warning bubble is unsupported on this platform.";
+}