* Electron Version: 3.0.0-beta.3
* Operating System Ubuntu 18.04
* Last known working Electron version: none  ... still fails on 2.0.5

**Expected Behavior**

Font Subpixel AA should work... only works when rendering a .HTML file, not via BrowserWindow.

**Actual behavior**

Subpixel AA only works when I load a .html file.. not a .js file.

**To Reproduce**

https://github.com/burtonator/electron3-fuzzy-text

Here is a repo.

This works:

```
./node_modules/.bin/electron test.html
```

This will fail:

```
./node_modules/.bin/electron index.js
```
The only way to actually see that it's failing is to use a zoom tool like ```kmag```

**Screenshots**

Here's loading the .html file on the command line. Notice the AA is working by the orange color on the outside of the text:

![image](https://user-images.githubusercontent.com/45447/43037663-8731acd2-8cc4-11e8-99bf-f2adfbfdecc4.png)

Here is the SAME text and same test.html file but I loaded it via BrowserWindow in my index.js script.

![image](https://user-images.githubusercontent.com/45447/43037676-a22fa30e-8cc4-11e8-8bee-4d20bdfde57f.png)

Electron fails to use AA text rendering in the new window.  

Hopefully this might help track down the bug.  


atom/browser/web_contents_preferences.cc
content::WebContents* web_contents,
    const mate::Dictionary& web_preferences)
    : web_contents_(web_contents) {
  v8::Isolate* isolate = web_preferences.isolate();
  mate::Dictionary copied(isolate, web_preferences.GetHandle()->Clone());
  
  copied.Delete("embedder");
  copied.Delete("isGuest");
  copied.Delete("session");
  mate::ConvertFromV8(isolate, copied.GetHandle(), &preference_);
  web_contents->SetUserData(UserDataKey(), base::WrapUnique(this));
  instances_.push_back(this);
  
  SetDefaultBoolIfUndefined(options::kPlugins, false);
  SetDefaultBoolIfUndefined(options::kExperimentalFeatures, false);
  bool node = SetDefaultBoolIfUndefined(options::kNodeIntegration, true);