[API] Implement register/unregister global desktop keyboard shortcut on Winodws.

- Introduce GlobalShortcutListener;
- New api object: Shortcut({'key': '...', 'active': ..., 'failed': ...});
- New api: App.registerGlobalHotkey, App.unregisterGlobalHotkey.
[Test] Manual test case for global keyboard shortcut.
[API] Finish register global desktop keyboard shortcut on linux.
[Test] Automatic test case for keyboard shortcut.
Remove DCHECK limitation of GlobalShortcutListener.
[API] Finish register global desktop keyboard shortcut on OSX.
Improvement: |key| of |Shortcut| should be case-insensitive.
Address comment: change {un}registerGlobalHotKey to sync method.
Fix build error of missing parameter: isolate.
X11ErrorTracker has been moved "ui/gfx/x/".
Append reference xhr in node context test case
Fix menu_shortcut test case on Windows
Merge pull request #2037 from gitchs/reference_xhr_in_node_context

Append reference xhr in node context test case
Merge pull request #2045 from gitchs/update-win-menu-shortcut-case

Update window menu shortcut test case.
Fixes typo.
Check URL before navigation

Fixed an error when an invalid url is given in the address bar.
Append http proxy auth test case.
Merge pull request #2047 from davidgomes/patch-1

Fixes typo.
Merge pull request #2054 from gitchs/http-proxy-auth

Append http proxy auth dialog test case
Merge pull request #1735 from zhchbin/hotkey

[API] Implement register/unregister global desktop keyboard shortcut.