WebLayerTreeView and WebWidget API cleanup

This CL consists of 3 orthogonal changes. None of the changes affect code
behavior.

[3/3] Use WebLayerTreeView::setNeedsAnimate in place of WebWidgetClient::scheduleAnimation

In single thread mode WebWidgetClient::scheduleAnimation will be routed through
SingleThreadProxy::SetNeedsAnimate. Now WebLayerTreeView::setNeedsAnimate
should work in both modes.

[2/3] Remove WebLayerTreeView::setNeedsRedraw

The implementation is fully equivalent to setNeedsAnimate.

[1/3] Remove WebWidget/WebViewImpl::setNeedsRedraw

BUG=112837

R=jamesr
DEPENDS=https://codereview.chromium.org/80173002/

Review URL: https://codereview.chromium.org/80203002

git-svn-id: svn://svn.chromium.org/blink/trunk@162572 bbb929c8-8fbe-4397-9dbb-9b2b20218538