[GTK] FullScreen signals

[GTK] FullScreen signals
https://bugs.webkit.org/show_bug.cgi?id=76181

Reviewed by Martin Robinson.

Source/WebKit/gtk:

Added entering-fullscreen and leaving-fullscreen signals, meant to
be used by the user agent to be notified when an element requests
full screen display and when the full screen display is to be
disabled.

* WebCoreSupport/ChromeClientGtk.cpp:
(WebKit::ChromeClient::supportsFullScreenForElement):
(WebKit::onFullscreenGtkKeyPressEvent):
(WebKit::ChromeClient::cancelFullScreen):
(WebKit::ChromeClient::enterFullScreenForElement):
(WebKit::ChromeClient::exitFullScreenForElement):
* WebCoreSupport/ChromeClientGtk.h:
* tests/testwebview.c:
* webkit/webkitwebview.cpp:
(webkit_web_view_real_entering_fullscreen):
(webkit_web_view_real_leaving_fullscreen):
(webkit_web_view_class_init):
* webkit/webkitwebview.h:

Tools:

Use the two new entering/leaving fullscreen signals to hide/show
the tool bar, the status bar and ask the user's permission before
entering fullscreen.

* GtkLauncher/main.c:
(webViewFullscreenMessageWindowClose):
(webViewWindowStateEvent):
(hide_widget):
(show_widget):
(webViewEnteringFullScreen):
(webViewLeavingFullScreen):
(createBrowser):
(createWindow):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108620 268f45cc-cd09-0410-ab3c-d52691b4dbfc