Replace NOTREACHED() with DCHECK(false) (fixes #3500)

Restores the old behavior of assertion in Debug build only.

libcef/browser/native/browser_platform_delegate_native_mac.mm

@@ -561,7 +561,7 @@ CefBrowserPlatformDelegateNativeMac::TranslateWebClickEvent(
       result.button = blink::WebMouseEvent::Button::kRight;
       break;
     default:
-      NOTREACHED();
+      DCHECK(false);
   }
 
   result.click_count = clickCount;