Oilpan: Completely move core/animations/ to oilpan's heap

The lifetime relationship between Animation objects are really complicated. The relationship in this CL is illustrated here:
https://docs.google.com/drawings/d/1jOs2hnSRDyVzH3CsEjdD8iq1hF9Kqt5KaZkMW_7Xv-U/edit?usp=sharing

BUG=340522

Review URL: https://codereview.chromium.org/225073004

git-svn-id: svn://svn.chromium.org/blink/trunk@174194 bbb929c8-8fbe-4397-9dbb-9b2b20218538