After creating a notification and passing a tag, then subsequent notifications with the same tag don't show up for the entire lifespan of the app.

* Electron version: 1.8.1
* Operating system: Windows 7 x64

### Expected behavior

New notifications should open after the last one has closed.

### Actual behavior

Nothing happens

### How to reproduce

  $ git clone https://github.com/electron/electron-quick-start .
  $ npm install
  $ npm start

Then in the app open dev tools and paste this in the console:

    new Notification("test", { tag: "test" });

Wait for the notification to disappear and paste it again, observe nothingness.
atom/browser/notifications/win/win32_desktop_notifications/toast.cc
is_content_updated_ = false;
}
bool DesktopNotificationController::Toast::IsRedrawNeeded() const {
  return !is_content_updated_;
}
void DesktopNotificationController::Toast::UpdateBufferSize() {
  if (hdc_) {
    SIZE new_size;
    {
      TEXTMETRIC tm_cap = {};
      HFONT font = data_->controller->GetCaptionFont();
      if (font) {
        SelectFont(hdc_, font);
        if (!GetTextMetrics(hdc_, &tm_cap))
          return;
      }
      TEXTMETRIC tm_body = {};
      font = data_->controller->GetBodyFont();
      if (font) {
        SelectFont(hdc_, font);
        if (!GetTextMetrics(hdc_, &tm_body))
          return;
      }
      this->margin_ = {tm_cap.tmAveCharWidth * 2, tm_cap.tmAscent / 2};
      new_size.cx = margin_.cx + (32 * tm_cap.tmAveCharWidth) + margin_.cx;