Oilpan: remove redundant WILL_BE_EAGERLY_TRACED() declarations.

With eager tracing of GC objects now being the default, remove
the WILL_BE_EAGERLY_TRACED() trait declarations added by r186410
for Web Animations related objects. Now redundant.

Not a straight revert of r186410, as it also tidied up some
tracing details for InterpolableValue subclasses; want to keep
those.

R=kouhei,haraken
BUG=420515

Review URL: https://codereview.chromium.org/791583002

git-svn-id: svn://svn.chromium.org/blink/trunk@186771 bbb929c8-8fbe-4397-9dbb-9b2b20218538
17 files changed