[Qt] Decide when to apply a scrolled position to the viewport based on the rect covered by the tiles
https://bugs.webkit.org/show_bug.cgi?id=97777

Reviewed by Kenneth Rohde Christiansen.

Source/WebCore:

* platform/graphics/TiledBackingStore.cpp:
(WebCore::TiledBackingStore::createTiles):
* platform/graphics/TiledBackingStore.h:
(WebCore::TiledBackingStore::coverRect):
(WebCore::TiledBackingStore::setCoverRect):
(TiledBackingStore):

Source/WebKit2:

This patch achieves two things:
- Apply a short scroll position request directly if we already have rendered tiles
  at this position.
- Since our visible rect request is asynchronous, the next frame might not always
  be the one covering this position. This will wait for a frame that does to apply it.

* UIProcess/API/qt/raw/qrawwebview_p_p.h:
(QRawWebViewPrivate::didRenderFrame):
* UIProcess/CoordinatedGraphics/LayerTreeCoordinatorProxy.cpp:
(WebKit::LayerTreeCoordinatorProxy::didRenderFrame):
* UIProcess/CoordinatedGraphics/LayerTreeCoordinatorProxy.h:
(LayerTreeCoordinatorProxy):
* UIProcess/CoordinatedGraphics/LayerTreeCoordinatorProxy.messages.in:
* UIProcess/PageClient.h:
(PageClient):
* UIProcess/PageViewportController.cpp:
(WebKit::PageViewportController::didCommitLoad):
(WebKit::PageViewportController::didRenderFrame):
(WebKit::PageViewportController::pageDidRequestScroll):
* UIProcess/PageViewportController.h:
(PageViewportController):
* UIProcess/WebPageProxy.h:
(WebPageProxy):
* UIProcess/qt/QtPageClient.cpp:
(WebKit::QtPageClient::didRenderFrame):
* UIProcess/qt/QtPageClient.h:
(QtPageClient):
* UIProcess/qt/WebPageProxyQt.cpp:
(WebKit::WebPageProxy::didRenderFrame):
* WebProcess/WebPage/CoordinatedGraphics/CoordinatedGraphicsLayer.h:
(WebCore::CoordinatedGraphicsLayer::coverRect):
* WebProcess/WebPage/CoordinatedGraphics/LayerTreeCoordinator.cpp:
(WebKit::LayerTreeCoordinator::flushPendingLayerChanges):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@130031 268f45cc-cd09-0410-ab3c-d52691b4dbfc