* Electron version: 1.6.1
* Operating system: MacOS 10.12

Create a webview, set the zoom level, then create a second webview for content at the same domain as the 1st webview.

### Expected behavior

Ideally the second webview would assume the same zoom as the existing webview. At minumum, it'd be good if the first webview maintained its current zoom.

### Actual behavior

The zoom level is reset on both webviews.

### How to reproduce

https://github.com/pfrazee/electron-bug-webview-zoom Instructions on the readme
atom/browser/web_contents_zoom_controller.h
#ifndef ATOM_BROWSER_WEB_CONTENTS_ZOOM_CONTROLLER_H_
#define ATOM_BROWSER_WEB_CONTENTS_ZOOM_CONTROLLER_H_
#include <map>
#include <string>
#include "content/public/browser/host_zoom_map.h"
#include "content/public/browser/web_contents_observer.h"
#include "content/public/browser/web_contents_user_data.h"
namespace atom {
class WebContentsZoomController