* Output of `node_modules/.bin/electron --version`: v3.0.0-beta.8
* Operating System (Platform and Version): Windows 10 10.0.16299 Build 16299
* Output of `node_modules/.bin/electron --version` on last known working Electron version (if applicable): v2.0.8

**Expected Behavior**
Webview DevTools should open in a window that is properly sized.

**Actual behavior**
Webview DevTools open in window with minimal size and are therefore not visible.

**To Reproduce**
**Edit** Works in BrowserWindow.webContents.openDevTools() Works **not** in webView.openDevTools()

**Screenshots**
![too_small_devtools_window](https://user-images.githubusercontent.com/6893212/44841398-850fed80-ac43-11e8-8bed-849d45473683.png)

**Additional Information**
Only reproducible on Windows 10 10.0.16299 Build 16299. Works correctly on MacOS High Sierra 10.13.4

brightray/browser/inspectable_web_contents_impl.cc
content::DevToolsAgentHost* agent_host,
    const std::string& message) {
  if (!frontend_loaded_)
    return;
  if (message.length() < kMaxMessageChunkSize) {
    base::string16 javascript =
        base::UTF8ToUTF16("DevToolsAPI.dispatchMessage(" + message + ");");
    GetDevToolsWebContents()->GetMainFrame()->ExecuteJavaScript(javascript);
    return;
  }
  base::Value total_size(static_cast<int>(message.length()));
  for (size_t pos = 0; pos < message.length(); pos += kMaxMessageChunkSize) {
    base::Value message_value(message.substr(pos, kMaxMessageChunkSize));
    CallClientFunction("DevToolsAPI.dispatchMessageChunk", &message_value,
                       pos ? nullptr : &total_size, nullptr);
  }
}
void InspectableWebContentsImpl::AgentHostClosed(
    content::DevToolsAgentHost* agent_host) {}
void InspectableWebContentsImpl::RenderFrameHostChanged(
    content::RenderFrameHost* old_host,
    content::RenderFrameHost* new_host) {
  if (new_host->GetParent())
    return;
  frontend_host_.reset(content::DevToolsFrontendHost::Create(
      new_host,
      base::Bind(&InspectableWebContentsImpl::HandleMessageFromDevToolsFrontend,
                 weak_factory_.GetWeakPtr())));
}
void InspectableWebContentsImpl::WebContentsDestroyed() {