Add window occlusion criteria to determine page visibility on Mac
https://bugs.webkit.org/show_bug.cgi?id=107494

Patch by Kiran Muppala <cmuppala@apple.com> on 2013-01-28
Reviewed by Simon Fraser.

Source/WebKit2:

* UIProcess/API/mac/PageClientImpl.mm:
(WebKit::PageClientImpl::isViewVisible): Add window occlusion check.
* UIProcess/API/mac/WKView.mm:
(-[WKView dealloc]): Remove self from the all views vector.
(-[WKView addWindowObserversForWindow:]): Register observer for
NSWindowWillOrderOffScreenNotification.
(-[WKView removeWindowObservers]): Unregister observer for
NSWindowWillOrderOffScreenNotification.
(-[WKView viewWillMoveToWindow:]): Disable occlusion notifications.
(-[WKView viewDidMoveToWindow]): Enable occlusion notifications.
(-[WKView _windowWillOrderOffScreen:]): Disable occlusion notifications.
(-[WKView _windowDidOrderOnScreen:]): Enable occlusion notifications.
This notification ensures that occlusion notifications are registered
correctly even if the NSWindow object is assigned a window number after
the viewDidMoveToWindow notification has been received.  This occurs
for instance during application launch.
(-[WKView _setIsWindowOccluded:]):
(-[WKView _enableWindowOcclusionNotifications]):
(-[WKView _disableWindowOcclusionNotifications]):
(windowBecameVisible):
(windowBecameOccluded):
(+[WKView _registerWindowOcclusionNotificationHandlers]):
(+[WKView _unregisterWindowOcclusionNotificationHandlers]):
(+[WKView _allViews]):
(-[WKView _isWindowOccluded]):
(-[WKView initWithFrame:contextRef:pageGroupRef:relatedToPage:]): Add
self to the all views vector.
* UIProcess/API/mac/WKViewInternal.h:

WebKitLibraries:

Add enum constants to specify window occlusion notification type to
notification registration/unregistration methods.  Add typedef for
window ID data passed to the window occlusion notification handler.
Add method to enable occlusion notifications for a particular window.

* WebKitSystemInterface.h: Add
WKOcclusionNotificationTypeWindowBecameVisible,
WKOcclusionNotificationTypeWindowBecameOccluded,
WKWindowID,
WKEnableWindowOcclusionNotifications().

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141045 268f45cc-cd09-0410-ab3c-d52691b4dbfc