Revert 168637 "Revert 168617 "Oilpan: Fix tracing of KeyframeVec..."

This was a mis-revert. Sorry, I'm relanding.

> Revert 168617 "Oilpan: Fix tracing of KeyframeVector in Composit..."
> 
> It broke build of Linux ChromiumOS Builder.
> 
> > Oilpan: Fix tracing of KeyframeVector in CompositorAnimationsTest.
> > 
> > R=haraken@chromium.org, oilpan-reviews@chromium.org
> > BUG=
> > 
> > Review URL: https://codereview.chromium.org/183923038
> 
> TBR=ager@chromium.org
> 
> Review URL: https://codereview.chromium.org/180033007

TBR=haraken@chromium.org

Review URL: https://codereview.chromium.org/183693013

git-svn-id: svn://svn.chromium.org/blink/trunk@168638 bbb929c8-8fbe-4397-9dbb-9b2b20218538