- Electron version: 1.2.8
- Operating system: Windows

Hi,

I've been trying to get a context menu containing some [predefined web contents roles](https://github.com/electron/electron/blob/master/lib/browser/api/menu-item-roles.js#L17) working for an application where we have multiple windows simultaneously. I've noticed that when a context menu is opened for a window that was created later than others, the role commands don't seem to execute when clicked. However, if don't use a role and instead define a click handler that calls the command on the web contents manually, it behaves normally.

I've been doing some digging and it seems that the reason is because, for a role, [`electron.webContents.getFocusedWebContents`](https://github.com/electron/electron/blob/master/lib/browser/api/web-contents.js#L257) is used to determine which web contents to call the command on (see [menu.js](https://github.com/electron/electron/blob/master/lib/browser/api/menu.js#L121)).

This function iterates through all existing web contents, then returns the first in the collection that is in a `webview`, otherwise the first that returns `true` from `contents.isFocused()`. However, it seems to be entirely possible that there are web contents other than the one that the context menu was raised for, who think they are focused (or perhaps are within a `webview`), and who were created earlier and therefore appear earlier in the collection.

This means there are situations when the 'wrong' web contents is returned from `getFocusedWebContents`, and therefore the role command is called on that 'wrong' web contents, which leads to the unexpected behaviour described above.

Is this a bug? And if so, is there a fix and/or workaround for this? I'm happy to contribute a PR if needed.

atom/browser/api/atom_api_web_contents.cc
v8::Local<v8::Value> val,
                     atom::SetSizeParams* out) {
    mate::Dictionary params;
    if (!ConvertFromV8(isolate, val, &params))
      return false;
    bool autosize;
    if (params.Get("enableAutoSize", &autosize))
      out->enable_auto_size.reset(new bool(true));
    gfx::Size size;
    if (params.Get("min", &size))
      out->min_size.reset(new gfx::Size(size));
    if (params.Get("max", &size))
      out->max_size.reset(new gfx::Size(size));
    if (params.Get("normal", &size))
      out->normal_size.reset(new gfx::Size(size));
    return true;
  }
};
template<>
struct Converter<PrintSettings> {
  static bool FromV8(v8::Isolate* isolate, v8::Local<v8::Value> val,