Add AppWindow.setVisibleOnAllWorkspaces.

extensions/renderer/resources/app_window_custom_bindings.js

Index: extensions/renderer/resources/app_window_custom_bindings.js
diff --git a/extensions/renderer/resources/app_window_custom_bindings.js b/extensions/renderer/resources/app_window_custom_bindings.js
index 812d3d6c6af54474773bc45892310b9ce48314e4..9020fb2e7ceafd20ca26bb1b93ba41b0e73d4b7d 100644
--- a/extensions/renderer/resources/app_window_custom_bindings.js
+++ b/extensions/renderer/resources/app_window_custom_bindings.js
@@ -193,6 +193,10 @@ appWindow.registerCustomHook(function(bindingsAPI) {
     return windows.length > 0 ? windows[0] : null;
   });
 
+  apiFunctions.setHandleRequest('canSetVisibleOnAllWorkspaces', function() {
+    return /Mac/.test(navigator.platform) || /Linux/.test(navigator.userAgent);
+  });
+
   // This is an internal function, but needs to be bound into a closure
   // so the correct JS context is used for global variables such as
   // currentWindowInternal, appWindowData, etc.