* 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
#include <memory>
#include <utility>
#include "brightray/browser/inspectable_web_contents_impl.h"
#include "atom/common/platform_util.h"
#include "base/guid.h"
#include "base/json/json_reader.h"
#include "base/json/json_writer.h"
#include "base/metrics/histogram.h"
#include "base/strings/pattern.h"
#include "base/strings/string_util.h"
#include "base/strings/stringprintf.h"
#include "base/strings/utf_string_conversions.h"
#include "base/values.h"
#include "brightray/browser/browser_client.h"
#include "brightray/browser/browser_context.h"
#include "brightray/browser/browser_main_parts.h"
#include "brightray/browser/inspectable_web_contents_delegate.h"
#include "brightray/browser/inspectable_web_contents_view.h"
#include "brightray/browser/inspectable_web_contents_view_delegate.h"
#include "components/prefs/pref_registry_simple.h"
#include "components/prefs/pref_service.h"
#include "components/prefs/scoped_user_pref_update.h"
#include "content/public/browser/browser_thread.h"
#include "content/public/browser/host_zoom_map.h"
#include "content/public/browser/navigation_handle.h"
#include "content/public/browser/render_frame_host.h"
#include "content/public/browser/render_view_host.h"
#include "content/public/common/user_agent.h"