* Electron version: 1.8.2
* Operating system: macos 10.13.3

Reproducing repo: https://github.com/ibash/electron-webkit-app-drag

Demonstrates a bug where `-webkit-app-region: drag` causes a browser view in front of it to miss click events. Oddly - it does not prevent hover events.

Steps:
1. Clone https://github.com/ibash/electron-webkit-app-drag, `yarn install`, `yarn start`
2. Click "button1"
3. Click "button2"

Expected:

Clicking button1 or button2 pops up an alert: "button clicked!"

Actual:

Only clicking button2 pops up an alert: "button clicked!"

atom/browser/api/atom_api_browser_window.cc
if (web_contents_.IsEmpty()) {
    return v8::Null(isolate);
  }
  return v8::Local<v8::Value>::New(isolate, web_contents_);
}
void BrowserWindow::RemoveFromParentChildWindows() {
  if (parent_window_.IsEmpty())
    return;
  mate::Handle<BrowserWindow> parent;
  if (!mate::ConvertFromV8(isolate(), GetParentWindow(), &parent)
    || parent.IsEmpty()) {
    return;
  }
  parent->child_windows_.Remove(ID());
}
std::unique_ptr<SkRegion> BrowserWindow::DraggableRegionsToSkRegion(
    const std::vector<DraggableRegion>& regions) {
  std::unique_ptr<SkRegion> sk_region(new SkRegion);
  for (const DraggableRegion& region : regions) {
    sk_region->op(
        region.bounds.x(),
        region.bounds.y(),
        region.bounds.right(),
        region.bounds.bottom(),
        region.draggable ? SkRegion::kUnion_Op : SkRegion::kDifference_Op);
  }
  return sk_region;
}
void BrowserWindow::ScheduleUnresponsiveEvent(int ms) {