Inform the tile cache whenever the visible rect changes

Inform the tile cache whenever the visible rect changes
https://bugs.webkit.org/show_bug.cgi?id=77470

Reviewed by Andreas Kling.

* platform/graphics/GraphicsLayer.h:
(WebCore::GraphicsLayer::visibleRectChanged):
Add empty function.

* platform/graphics/ca/GraphicsLayerCA.cpp:
(WebCore::GraphicsLayerCA::visibleRectChanged):
Call through to the PlatformCALayer.

* platform/graphics/ca/mac/PlatformCALayerMac.mm:
(PlatformCALayer::visibleRectChanged):
Call through to the underlying WebTileCacheLayer.

* platform/graphics/ca/mac/TileCache.mm:
(WebCore::TileCache::visibleRectChanged):
Add empty stub.

(WebCore::TileCache::visibleRect):
Add new (currently unused) helper function that returns the visible rect of the
tile cache layer.

* platform/graphics/ca/mac/WebTileCacheLayer.h:
* platform/graphics/ca/mac/WebTileCacheLayer.mm:
(-[WebTileCacheLayer visibleRectChanged]):
Call through to the TielCache object.

* platform/graphics/ca/win/PlatformCALayerWin.cpp:
(PlatformCALayer::visibleRectChanged):
Add stub.

* rendering/RenderLayerCompositor.cpp:
(WebCore::RenderLayerCompositor::frameViewDidScroll):
Call GraphicsLayer::visibleRectChanged.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@106385 268f45cc-cd09-0410-ab3c-d52691b4dbfc