Add scrolling related getters to WebLayerImpl

Add scrolling related getters to WebLayerImpl

This patch adds a number of scrolling related getters to WebLayerImpl
and LayerChromium for testing purposes. They will be used by the
ScrollingCoordinatorChromium test (http://webkit.org/b/96657).

Note that the WebLayerImpl getters aren't marked with OVERRIDE because
the corresponding changes to WebLayer aren't in place yet. This will be
corrected later.

BUG=none


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=157101

[jamesr, 2012-09-14 19:51:11]

lgtm

don't feel obligated to add OVERRIDE, having them in place makes N-sided patches
much harder to deal with

[commit-bot: I haz the power, 2012-09-17 09:22:16]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/skyostil@chromium.org/10909233/1

[commit-bot: I haz the power, 2012-09-17 11:43:06]

Change committed as 157101