- Electron version: v1.3.3
- Operating system: OS X 10.11.6

v1.3.3 broke the detection of the `scroll-touch-begin` and `scroll-touch-end` events for me within a `webview`. It looks like the pull request #6754 caused this issue. v1.3.2 works as expected.

Behavior that I'm observing on v1.3.3:
- Most of the time, the `scroll-touch-*` events are not emitted when the cursor is on top of a `webview`.
- The `scroll-touch-*` events seem to be emitted _only once_ when the cursor is on a `webview` and on a scrollable element. The scrollable elements in my app have no native scrollbar set (they have the style `overflow: hidden;` set instead of `overflow: scroll;`). This is the case in which I need to receive the `scroll-touch-*` events.
- The `scroll-touch-*` events seem to work fine when the cursor is outside of the `webview` tag.

atom/browser/native_window_mac.h
void SetTitle(const std::string& title) override;
  std::string GetTitle() override;
  void FlashFrame(bool flash) override;
  void SetSkipTaskbar(bool skip) override;
  void SetKiosk(bool kiosk) override;
  bool IsKiosk() override;
  void SetBackgroundColor(const std::string& color_name) override;
  void SetHasShadow(bool has_shadow) override;
  bool HasShadow() override;
  void SetRepresentedFilename(const std::string& filename) override;
  std::string GetRepresentedFilename() override;
  void SetDocumentEdited(bool edited) override;
  bool IsDocumentEdited() override;
  void SetIgnoreMouseEvents(bool ignore) override;
  void SetContentProtection(bool enable) override;
  void SetParentWindow(NativeWindow* parent) override;
  gfx::NativeWindow GetNativeWindow() override;
  gfx::AcceleratedWidget GetAcceleratedWidget() override;
  void SetProgressBar(double progress, const ProgressState state) override;
  void SetOverlayIcon(const gfx::Image& overlay,
                      const std::string& description) override;
  void SetVisibleOnAllWorkspaces(bool visible) override;
  bool IsVisibleOnAllWorkspaces() override;
  
  void OnInputEvent(const blink::WebInputEvent& event) override;
  
  void RenderViewHostChanged(content::RenderViewHost* old_host,
                             content::RenderViewHost* new_host) override;
  
  void UpdateDraggableRegionViews() {