https://bugs.webkit.org/show_bug.cgi?id=94417

Reviewed by Carlos Garcia Campos.

Instead of rendering directly to the widget's native window, render to an
offscreen window redirected to a Pixmap with XComposite.

Source/WebCore:

No new tests. This will be covered by the existing accelerated compositing tests,
which should now give correct pixel results.

* platform/gtk/RedirectedXCompositeWindow.cpp:
(WebCore::RedirectedXCompositeWindow::resize): Add a call to XFlush which ensures
that pending X11 operations complete.
* platform/gtk/RedirectedXCompositeWindow.h:
(WebCore::RedirectedXCompositeWindow::windowId): Added this accessor.

Source/WebKit2:

* UIProcess/API/gtk/WebKitWebViewBase.cpp:
(_WebKitWebViewBasePrivate): Added a few members necessary to track the
offscreen window.
(webkit_web_view_base_init):
(renderAcceleratedCompositingResults): Added this helper functions which renders
the results of the accelerated compositing operations during the GTK+ draw loop.
(webkitWebViewBaseDraw): Call renderAcceleratedCompositingResults when appropriate.
(resizeWebKitWebViewBaseFromAllocation): Resize the offscreen window when appropriate.
(webkitWebViewBaseSizeAllocate): Do not call resizeWebKitWebViewBaseFromAllocation when
the actual size of the widget does not change. This prevents destroying and recreating
the offscreen window pixmap when it isn't necessary.
(webkitWebViewBaseMap): We no longer send the window id during map, instead it's sent
as soon as there is WebPageProxy.
(webkitWebViewBaseCreateWebPage): Send the window id of the redirected window to
the WebProcess.
(queueAnotherDrawOfAcceleratedCompositingResults): Added this helper which works
around the issue of slow updates of the pixmap backing the redirected XComposite window.
(webkitWebViewBaseQueueDrawOfAcceleratedCompositingResults): Added this method which
is what the WebProcess uses to force a redraw on the UIProcess side.
* UIProcess/API/gtk/WebKitWebViewBasePrivate.h: Added new method to the list of private methods.
* UIProcess/DrawingAreaProxyImpl.h:
(DrawingAreaProxyImpl):
(WebKit::DrawingAreaProxyImpl::isInAcceleratedCompositingMode): Exposed this method publically
so that it can be used from WebKitWebViewBase.
* UIProcess/WebPageProxy.h:
(WebPageProxy): Renamed widgetMapped to setAcceleratedCompositingWindowId.
* UIProcess/WebPageProxy.messages.in: Ditto.
* UIProcess/gtk/WebPageProxyGtk.cpp: Ditto.
(WebKit::WebPageProxy::setAcceleratedCompositingWindowId):
* WebProcess/WebPage/WebPage.h:
(WebPage): Ditto.
* WebProcess/WebPage/WebPage.messages.in: Ditto.
* WebProcess/WebPage/gtk/LayerTreeHostGtk.cpp:
(WebKit::LayerTreeHostGtk::sizeDidChange): Force a composite to the resized window right
away so that the new window pixmap is updated before the first draw.
(WebKit::LayerTreeHostGtk::compositeLayersToContext): If the composition is for a resize,
first clear the entire GL context so that we don't see black artifacts during resize.
* WebProcess/WebPage/gtk/LayerTreeHostGtk.h:
(LayerTreeHostGtk): Update the signature of  compositeLayersToContext.
* WebProcess/WebPage/gtk/WebPageGtk.cpp:
(WebKit::WebPage::setAcceleratedCompositingWindowId): Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@128907 268f45cc-cd09-0410-ab3c-d52691b4dbfc