https://bugs.webkit.org/show_bug.cgi?id=121874
<rdar://problem/15071494>

Reviewed by Sam Weinig.

* Shared/DrawingAreaInfo.h:
We can have DrawingAreaTypeTiledCoreAnimation without threaded scrolling.

* Shared/WebPreferencesStore.h:
* UIProcess/API/C/WKPreferences.cpp:
(WKPreferencesSetThreadedScrollingEnabled):
(WKPreferencesGetThreadedScrollingEnabled):
* UIProcess/API/C/WKPreferencesPrivate.h:
Add a preference for threaded scrolling.

* UIProcess/API/mac/WKView.mm:
(-[WKView WebKit::]):
* UIProcess/mac/TiledCoreAnimationDrawingAreaProxy.h:
* UIProcess/mac/TiledCoreAnimationDrawingAreaProxy.mm:
* WebProcess/WebPage/DrawingArea.cpp:
(WebKit::DrawingArea::create):
* WebProcess/WebPage/DrawingArea.h:
Make it so we can use TiledCoreAnimationDrawingArea without ENABLE(THREADED_SCROLLING).

* WebProcess/WebCoreSupport/WebChromeClient.cpp:
(WebKit::WebChromeClient::shouldUseTiledBackingForFrame):
* WebProcess/WebCoreSupport/WebChromeClient.h:
Override shouldUseTiledBackingForFrame; ask the drawing area if we want a tiled backing for the given frame.

* WebProcess/WebPage/WebPage.cpp:
(WebKit::WebPage::WebPage):
(WebKit::WebPage::~WebPage):
* WebProcess/WebPage/WebPage.h:
Move attaching and detaching the scrolling tree into WebPage.
Store whether or not this page is going to use threaded scrolling once, as this
cannot change through the life of a page.

* WebProcess/WebPage/mac/TiledCoreAnimationDrawingArea.h:
* WebProcess/WebPage/mac/TiledCoreAnimationDrawingArea.mm:
(WebKit::TiledCoreAnimationDrawingArea::TiledCoreAnimationDrawingArea):
(WebKit::TiledCoreAnimationDrawingArea::~TiledCoreAnimationDrawingArea):
Move attaching and detaching the scrolling tree into WebPage.

(WebKit::TiledCoreAnimationDrawingArea::didInstallPageOverlay):
(WebKit::TiledCoreAnimationDrawingArea::didUninstallPageOverlay):
(WebKit::TiledCoreAnimationDrawingArea::updatePreferences):
(WebKit::TiledCoreAnimationDrawingArea::dispatchAfterEnsuringUpdatedScrollPosition):
Only do scrolling coordinator work if we have a scrolling coordinator.

(WebKit::TiledCoreAnimationDrawingArea::shouldUseTiledBackingForFrame):
TiledCoreAnimationDrawingArea always wants a tiled backing for the main frame.

No new tests; a near-future patch is going to put the majority of layout
tests into the tiled-drawing-without-threaded-scrolling mode.

* page/ChromeClient.h:
(WebCore::ChromeClient::shouldUseTiledBackingForFrame):
Add a ChromeClient callback to determine whether a given frame wants a TiledBacking for its contents.

* page/FrameView.h:
* WebCore.exp.in:
Make isMainFrameView public and export it for use in WebKit2.

* rendering/RenderLayerBacking.cpp:
(WebCore::RenderLayerBacking::RenderLayerBacking):
Make use of shouldUseTiledBackingForFrame instead of predicating the
main frame using a tile cache on whether we have a scrolling coordinator.

* rendering/RenderLayerCompositor.cpp:
(WebCore::RenderLayerCompositor::mainFrameBackingIsTiled): Added.

(WebCore::RenderLayerCompositor::shouldCompositeOverflowControls):
(WebCore::RenderLayerCompositor::requiresOverhangAreasLayer):
(WebCore::RenderLayerCompositor::requiresContentShadowLayer):
All of these checks for existence of a scrollingCoordinator should actually
key off whether we're using tiled drawing at the root; they have nothing
to do with threaded scrolling.

* rendering/RenderLayerCompositor.h:

* WebKitTestRunner/mac/PlatformWebViewMac.mm:
(WTR::PlatformWebView::PlatformWebView):
The existing tiled-drawing layout tests require threaded scrolling to be enabled.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@156472 268f45cc-cd09-0410-ab3c-d52691b4dbfc