* Electron version: 2.0.0beta3 & 1.8.3
* Operating system: OSX & Windows 10 64bit

### Expected behavior

Resizing a nativeImage that is a product of calling BrowserWindow.capturePage should maintain transparency in all cases, not just when hardware acceleration is disabled

### Actual behavior
Resizing a nativeImage that is a product of calling BrowserWindow.capturePage converts tranparent pixels to black. If you instantiate your app disabling the gpu / hardware acceleration (app.disableHardwareAcceleration) it works as one would expect.

### How to reproduce
```
git clone https://github.com/countravioli/electron-native-image-resize-transparency-bug
cd electron-native-image-resize-transparency-bug
npm install
npm start
npm run start-works
```

npm start - will run the app normally, illustrating the bug. Two images are written in the directory at the same level as app.js (original.png and resized.png)
npm run start-works - will run the app with disableHardwareAcceleration showing things work. The same to pngs are created.

The app will quit when its done. If you are on mac the pngs will open in your default application associated with the file type. 

atom/browser/api/atom_api_web_contents.cc
if (managed_web_contents()) {
    managed_web_contents()->GetView()->SetDelegate(nullptr);
    
    
    if (type_ == WEB_VIEW)
      guest_delegate_->Destroy();
    RenderViewDeleted(web_contents()->GetRenderViewHost());
    if (type_ == WEB_VIEW) {
      DestroyWebContents(false );
    } else {
      if (type_ == BROWSER_WINDOW && owner_window()) {
        for (ExtendedWebContentsObserver& observer : observers_)
          observer.OnCloseContents();
      } else {
        DestroyWebContents(true );
      }
      
      
      
      WebContentsDestroyed();
    }
  }
}
void WebContents::DestroyWebContents(bool async) {