Coordinated Graphics: remove the DidChangeScrollPosition message.

Coordinated Graphics: remove the DidChangeScrollPosition message.
https://bugs.webkit.org/show_bug.cgi?id=108051

Patch by Huang Dongsung <luxtella@company100.net> on 2013-02-11
Reviewed by Noam Rosenthal.
Signed off for WebKit2 by Benjamin Poulain.

Currently, we use the DidChangeScrollPosition message to send the scroll
position that WebCore used in this frame to UI Process. We had to have
some member variables for the DidChangeScrollPosition message.
However, we can send a scroll position via the DidRenderFrame message,
because CoordinatedGraphicsScene::m_renderedContentsScrollPosition is
updated at the moment of flushing. So we can remove the
DidChangeScrollPosition message and some redundant member variables.

Source/WebCore:

No tests. No change in behavior.

* platform/graphics/texmap/coordinated/CoordinatedGraphicsScene.cpp:
(WebCore::CoordinatedGraphicsScene::flushLayerChanges):
* platform/graphics/texmap/coordinated/CoordinatedGraphicsScene.h:
(CoordinatedGraphicsScene):

Source/WebKit2:

* UIProcess/CoordinatedGraphics/CoordinatedLayerTreeHostProxy.cpp:
(WebKit::CoordinatedLayerTreeHostProxy::didRenderFrame):
(WebKit):
* UIProcess/CoordinatedGraphics/CoordinatedLayerTreeHostProxy.h:
(CoordinatedLayerTreeHostProxy):
* UIProcess/CoordinatedGraphics/CoordinatedLayerTreeHostProxy.messages.in:
  Remove the DidChangeScrollPosition message.
* WebProcess/WebPage/CoordinatedGraphics/CoordinatedLayerTreeHost.cpp:
(WebKit::CoordinatedLayerTreeHost::CoordinatedLayerTreeHost):
(WebKit::CoordinatedLayerTreeHost::flushPendingLayerChanges):
  Send a scroll position via the DidChangeScrollPosition message.
(WebKit::CoordinatedLayerTreeHost::syncLayerState):
  Don't send a scroll position because flushPendingLayerChanges() does
  that. In addition, it is weird to check if we must send a scroll
  position at the moment of sending the SyncLayerState message of every
  layers.
(WebKit::CoordinatedLayerTreeHost::setVisibleContentsRect):
* WebProcess/WebPage/CoordinatedGraphics/CoordinatedLayerTreeHost.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@142578 268f45cc-cd09-0410-ab3c-d52691b4dbfc