* 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::NavigationHandle* navigation_handle) {
  if (navigation_handle->IsInMainFrame() ||
      !navigation_handle->GetURL().SchemeIs("chrome-extension") ||
      !navigation_handle->HasCommitted())
    return;
  content::RenderFrameHost* frame = navigation_handle->GetRenderFrameHost();
  auto origin = navigation_handle->GetURL().GetOrigin().spec();
  auto it = extensions_api_.find(origin);
  if (it == extensions_api_.end())
    return;
  
  
  base::ReplaceFirstSubstringAfterOffset(&it->second, 0, "var chrome",
                                         "var chrome = window.chrome ");
  auto script = base::StringPrintf("%s(\"%s\")", it->second.c_str(),
                                   base::GenerateGUID().c_str());
  
  
  frame->ExecuteJavaScriptForTests(base::UTF8ToUTF16(script));
}
void InspectableWebContentsImpl::OnURLFetchComplete(