title: electron browserwindow useContentSize doesn't work
body: <p>When I create a BrowserWindow in electron, I want use the html size as the BrowserWindow  size instead of assigning width and height to it. So I set 'useContentSize:true', but the browserwindow size is default 800*600, it seems useContentSize doesn't work, does someone meet this problem?</p>
  
  <p>here is my code of creating BrowserWindow</p>
  
  <pre>   
  
        var mainWindow = new BrowserWindow({   
          frame: false,
          show: false,
          useContentSize: true
        })  
  
  </pre>
  
  <p>and this is the html page for BrowserWindow to load </p>
  
  <pre>     
  
      body {
          width: 300px;
          height: 300px;
          background-color: red;
          margin: 0px;
          padding: 0px;
      }      
      div {
          width: 100%;
          height: 100%;
          background-color: green;
          -webkit-app-region: drag;
      }
  
  </pre>
  
  <p>so when I use 'useContentSize: true', the BrowserWindow  should be 300*300,
   but the BrowserWindow is actually 800*600</p>
  
  <p>and there is a screenshot</p>
  
  <p><a href="https://i.stack.imgur.com/acI3i.png" rel="nofollow noreferrer">electron browserwindow 'useContentSize:true'</a></p>