* Electron Version: 2.0.0
* Operating System (Platform and Version): Windows 10
* Last known working Electron version:  N/A

**Expected Behavior**
If the last focusable HTML element is focused and I press 'tab', then the next thing that is focused should either be the first focusable HTML element, or if not, then whatever is focused should have a visible focus.

**Actual behavior**
Something is being focused (I think it is the entire HTML document?) and there is no visual indication as to what it is. It is fine that this other thing is being focused, what is not fine is that I/a user does not know where the keyboard focus has gone.

**To Reproduce**
- Checkout the [electron-quick-start](https://github.com/electron/electron-quick-start)- Put an `<input type="text"/>` before the `renderer.js` script
- Launch quick start
- Set focus in the input
- Press 'tab'


atom/browser/common_web_contents_delegate.cc
#include "atom/browser/common_web_contents_delegate.h"
#include <memory>
#include <set>
#include <string>
#include <utility>
#include <vector>
#include "atom/browser/atom_browser_context.h"
#include "atom/browser/native_window.h"
#include "atom/browser/ui/file_dialog.h"
#include "atom/browser/web_contents_preferences.h"
#include "atom/browser/web_dialog_helper.h"
#include "atom/common/atom_constants.h"
#include "atom/common/options_switches.h"
#include "base/files/file_util.h"
#include "base/json/json_reader.h"
#include "base/task/post_task.h"
#include "base/threading/sequenced_task_runner_handle.h"
#include "chrome/browser/ssl/security_state_tab_helper.h"