old_contents: import React from 'react'
  import { inject, observer } from 'mobx-react'
  import DraggableTab from './Tab/DraggableTab'
  
  @inject('tabStore')
  @observer
  export default class DragPreview extends React.Component {
    render () {
      const { tabStore: { sources }, setDragPreview } = this.props
      const content = sources.map((tab) => (
        <DraggableTab key={tab.id} {...tab} faked />
      ))
      return (
        <div
          ref={setDragPreview}
          style={{
            position: 'fixed',
            top: 2048
          }}>
          {content}
        </div>
      )
    }
  }
  
new_contents: import React from 'react'
  import { inject, observer } from 'mobx-react'
  import DraggableTab from './Tab/DraggableTab'
  import { blue } from 'material-ui/colors'
  
  @inject('tabStore')
  @observer
  export default class DragPreview extends React.Component {
    render () {
      const { tabStore: { sources }, setDragPreview } = this.props
      const content = sources.map((tab) => (
        <DraggableTab key={tab.id} {...tab} faked />
      ))
      return (
        <div
          ref={setDragPreview}
          style={{
            width: '64%',
            position: 'fixed',
            background: blue[100],
            textAlign: 'center',
            top: 2048
          }}>
          <h3>
            {sources.length} tab{sources.length > 1 && 's'}
          </h3>
          {content}
        </div>
      )
    }
  }
  
subject: Add title for DragPreview