* Electron version: 1.6.0
* Operating system: MacOS 10.12.2

### Expected behavior

'scroll-touch-end' emits when trackpad scrolling ends.

### Actual behavior

The begin event emits, but not the end

### How to reproduce

Example repo: https://github.com/pfrazee/electron-bug-no-scroll-touch-end

atom/browser/native_window.cc
for (NativeWindowObserver& observer : observers_)
    observer.OnWindowScrollTouchEdge();
}
void NativeWindow::NotifyWindowScrollTouchEdge() {
  for (NativeWindowObserver& observer : observers_)
    observer.OnWindowScrollTouchEdge();
}
void NativeWindow::NotifyWindowSwipe(const std::string& direction) {
  for (NativeWindowObserver& observer : observers_)
    observer.OnWindowSwipe(direction);
}
void NativeWindow::NotifyWindowLeaveFullScreen() {
  for (NativeWindowObserver& observer : observers_)
    observer.OnWindowLeaveFullScreen();
}
void NativeWindow::NotifyWindowEnterHtmlFullScreen() {
  for (NativeWindowObserver& observer : observers_)
    observer.OnWindowEnterHtmlFullScreen();
}
void NativeWindow::NotifyWindowLeaveHtmlFullScreen() {
  for (NativeWindowObserver& observer : observers_)
    observer.OnWindowLeaveHtmlFullScreen();
}
void NativeWindow::NotifyWindowExecuteWindowsCommand(
    const std::string& command) {
  for (NativeWindowObserver& observer : observers_)
    observer.OnExecuteWindowsCommand(command);
}
#if defined(OS_WIN)
void NativeWindow::NotifyWindowMessage(