<!--
Thanks for opening an issue! A few things to keep in mind:

- The issue tracker is only for bugs and feature requests.
- Before reporting a bug, please try reproducing your issue against
  the latest version of Electron.
- If you need general advice, join our Slack: http://atom-slack.herokuapp.com
-->

# Description

* Electron version: 1.8.4
* Operating system: Windows 10

Calling `webContents.sendInputEvent` with type as `"char"` to a document containing a webview is rendered offscreen and an input panel is focused

<!-- What do you think should happen? -->

# Expected result

Keyboard input should be placed into the input panel

<!-- What actually happens? -->

# Actual result

Electron crashes

<!-- 

Your best chance of getting this bug looked at quickly is to provide a REPOSITORY that can be cloned and run.

You can fork https://github.com/electron/electron-quick-start and include a link to the branch with your changes.

If you provide a URL, please list the commands required to clone/setup/run your repo e.g.

  $ git clone $YOUR_URL -b $BRANCH
  $ npm install
  $ npm start || electron .

-->

# Repro steps

[I have a repo set up that will demonstrate the issue.](https://github.com/ImOnALampshade/electron-webview-char-crash) Clone that to see. Read the readme in that for more information.

```bash
git clone https://github.com/ImOnALampshade/electron-webview-char-crash.git
npm install
npm start
```
atom/browser/api/atom_api_web_contents.cc
zoom_controller_->SetZoomLevel(level);
}
double WebContents::GetZoomLevel() {
  return zoom_controller_->GetZoomLevel();
}
void WebContents::SetZoomFactor(double factor) {
  auto level = content::ZoomFactorToZoomLevel(factor);
  SetZoomLevel(level);
}
double WebContents::GetZoomFactor() {
  auto level = GetZoomLevel();
  return content::ZoomLevelToZoomFactor(level);
}
void WebContents::OnSetTemporaryZoomLevel(content::RenderFrameHost* rfh,
                                          double level,
                                          IPC::Message* reply_msg) {
  zoom_controller_->SetTemporaryZoomLevel(level);
  double new_level = zoom_controller_->GetZoomLevel();
  AtomFrameHostMsg_SetTemporaryZoomLevel::WriteReplyParams(reply_msg,
                                                           new_level);
  rfh->Send(reply_msg);
}
void WebContents::OnGetZoomLevel(content::RenderFrameHost* rfh,
                                 IPC::Message* reply_msg) {
  AtomFrameHostMsg_GetZoomLevel::WriteReplyParams(reply_msg, GetZoomLevel());
  rfh->Send(reply_msg);
}
v8::Local<v8::Value> WebContents::GetWebPreferences(v8::Isolate* isolate) {