* 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 "ipc/ipc_channel.h"
#include "net/http/http_response_headers.h"
#include "net/url_request/url_fetcher.h"
#include "net/url_request/url_fetcher_response_writer.h"
#include "ui/display/display.h"
#include "ui/display/screen.h"
namespace brightray {
namespace {
const double kPresetZoomFactors[] = {0.25, 0.333, 0.5,  0.666, 0.75, 0.9,
                                     1.0,  1.1,   1.25, 1.5,   1.75, 2.0,
                                     2.5,  3.0,   4.0,  5.0};
const char kChromeUIDevToolsURL[] =
    "chrome-devtools://devtools/bundled/devtools_app.html?"
    "remoteBase=%s&"
    "can_dock=%s&"
    "toolbarColor=rgba(223,223,223,1)&"
    "textColor=rgba(0,0,0,1)&"
    "experiments=true";
const char kChromeUIDevToolsRemoteFrontendBase[] =
    "https://chrome-devtools-frontend.appspot.com/";
const char kChromeUIDevToolsRemoteFrontendPath[] = "serve_file";
const char kDevToolsBoundsPref[] = "brightray.devtools.bounds";
const char kDevToolsZoomPref[] = "brightray.devtools.zoom";
const char kDevToolsPreferences[] = "brightray.devtools.preferences";
const char kFrontendHostId[] = "id";
const char kFrontendHostMethod[] = "method";
const char kFrontendHostParams[] = "params";
const char kTitleFormat[] = "Developer Tools - %s";
const size_t kMaxMessageChunkSize = IPC::Channel::kMaximumMessageSize / 4;
void RectToDictionary(const gfx::Rect& bounds, base::DictionaryValue* dict) {