<!--
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
if (!files.empty()) {
    base::MessageLoop::ScopedNestableTaskAllower allow(
        base::MessageLoop::current());
    DragFileItems(files, icon->image(), web_contents()->GetNativeView());
  } else {
    args->ThrowError("Must specify either 'file' or 'files' option");
  }
}
void WebContents::CapturePage(mate::Arguments* args) {
  gfx::Rect rect;
  base::Callback<void(const gfx::Image&)> callback;
  if (!(args->Length() == 1 && args->GetNext(&callback)) &&
      !(args->Length() == 2 && args->GetNext(&rect) &&
        args->GetNext(&callback))) {
    args->ThrowError();
    return;
  }
  auto* const view = web_contents()->GetRenderWidgetHostView();
  if (!view) {
    callback.Run(gfx::Image());
    return;
  }
  
  const gfx::Size view_size =
      rect.IsEmpty() ? view->GetViewBounds().size() : rect.size();
  
  
  
  gfx::Size bitmap_size = view_size;
  const gfx::NativeView native_view = view->GetNativeView();