[iOS WK2] Missing content inside long overflow-scrolling:touch

[iOS WK2] Missing content inside long overflow-scrolling:touch
https://bugs.webkit.org/show_bug.cgi?id=132105

Reviewed by Tim Horton.

PlatformCALayerRemote needs to track bounds origin as well as size,
since iOS uses bounds origin for overflow scrolling.

* Shared/mac/RemoteLayerTreePropertyApplier.mm:
(WebKit::applyPropertiesToLayer):
* Shared/mac/RemoteLayerTreeTransaction.h:
* Shared/mac/RemoteLayerTreeTransaction.mm:
(WebKit::RemoteLayerTreeTransaction::LayerProperties::LayerProperties):
(WebKit::RemoteLayerTreeTransaction::LayerProperties::encode):
(WebKit::RemoteLayerTreeTransaction::LayerProperties::decode):
(WebKit::dumpChangedLayers):
* WebProcess/WebPage/mac/PlatformCALayerRemote.cpp:
(WebKit::PlatformCALayerRemote::updateBackingStore):
(WebKit::PlatformCALayerRemote::bounds):
(WebKit::PlatformCALayerRemote::setBounds):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@167749 268f45cc-cd09-0410-ab3c-d52691b4dbfc