https://bugs.webkit.org/show_bug.cgi?id=125803

Reviewed by Anders Carlsson.

When the view state of the page is updated the layer mode may also
change. Currently this is passed by a separate message, remove this
and fold it into ViewState.
        
Previously the setLayerHostingMode message would be passed to the
DrawingArea, which would inform the WebPage. Since the WebPage is
passed the SetVisibilityState messgae reverse this.

WebPageProxy had a policy of only updating the hosting mode when
visible - the value is sticky whilst the view is not visible. Make
this policy explicit in the PageClientImpl, rather then implicit
from the flow control.

* Shared/ViewState.h:
    - Added ViewState::IsLayerWindowServerHosted.
* Shared/WebPageCreationParameters.cpp:
(WebKit::WebPageCreationParameters::encode):
(WebKit::WebPageCreationParameters::decode):
* Shared/WebPageCreationParameters.h:
    - removed layerHostingMode.
* UIProcess/API/mac/PageClientImpl.h:
* UIProcess/API/mac/PageClientImpl.mm:
(WebKit::PageClientImpl::PageClientImpl):
(WebKit::PageClientImpl::isLayerWindowServerHosted):
(WebKit::PageClientImpl::viewWillMoveToAnotherWindow):
    - viewLayerHostingMode -> isLayerWindowServerHosted, added m_layerHostingMode.
* UIProcess/DrawingAreaProxy.h:
    - removed layerHostingModeDidChange.
* UIProcess/PageClient.h:
    - viewLayerHostingMode -> isLayerWindowServerHosted.
* UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::WebPageProxy):
    - removed m_layerHostingMode.
(WebKit::WebPageProxy::updateViewState):
    - added IsLayerWindowServerHosted.
(WebKit::WebPageProxy::viewStateDidChange):
    - changes to ViewState::IsInWindow implies ViewState::IsLayerWindowServerHosted may change too.
    - remove special handling (separate message) for LayerHostingMode.
(WebKit::WebPageProxy::initializeCreationParameters):
    - removed m_layerHostingMode.
* UIProcess/WebPageProxy.h:
    - removed m_layerHostingMode.
* UIProcess/mac/TiledCoreAnimationDrawingAreaProxy.h:
* UIProcess/mac/TiledCoreAnimationDrawingAreaProxy.mm:
    - removed layerHostingModeDidChange.
* WebProcess/WebPage/DrawingArea.h:
(WebKit::DrawingArea::setLayerHostingMode):
(WebKit::DrawingArea::didUpdate):
    - setLayerHostingMode takes a LayerHostingMode.
* WebProcess/WebPage/DrawingArea.messages.in:
    - SetLayerHostingMode is no longer a message.
* WebProcess/WebPage/WebPage.cpp:
(WebKit::WebPage::WebPage):
    - removed m_layerHostingMode.
(WebKit::WebPage::setViewState):
    - handle ViewState::IsLayerWindowServerHosted.
(WebKit::WebPage::setLayerHostingMode):
    - moved from ~Mac.mm (matching other ViewState setters), calls to DrawingArea.
* WebProcess/WebPage/WebPage.h:
(WebKit::WebPage::layerHostingMode):
    - layerHostingMode queries m_viewState, removed m_layerHostingMode.
* WebProcess/WebPage/ios/WebPageIOS.mm:
    - removed setLayerHostingMode.
* WebProcess/WebPage/mac/TiledCoreAnimationDrawingArea.h:
* WebProcess/WebPage/mac/TiledCoreAnimationDrawingArea.mm:
(WebKit::TiledCoreAnimationDrawingArea::setLayerHostingMode):
    - setLayerHostingMode takes a LayerHostingMode, WebPage now calls to DrawingArea.
* WebProcess/WebPage/mac/WebPageMac.mm:
    - removed setLayerHostingMode.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@160695 268f45cc-cd09-0410-ab3c-d52691b4dbfc