Move FrameView::serviceScriptedAnimations to a Page-level object

FrameView::serviceScriptedAnimations is only ever called on the top-level
FrameView. It walks the whole frame heirachy and services all the animations
for every document.

This CL moves that function to a Page-level object, which means its associated
state, m_servicingAnimations, will exist only once per frame heirarchy (instead
of existing incorrectly at every level of the heirarchy).

R=ojan@chromium.org

Review URL: https://codereview.chromium.org/175053005

git-svn-id: svn://svn.chromium.org/blink/trunk@167607 bbb929c8-8fbe-4397-9dbb-9b2b20218538