Revert of Use count strings as keyframes/animation-name identifiers (patchset #2 id:20001 of https://codereview.chromium.org/651123003/)

Reason for revert:
Seems to cause crash: 
https://code.google.com/p/chromium/issues/detail?id=424520

Original issue's description:
> Use count strings as keyframes/animation-name identifiers
> 
> Strings are not valid keyframes/animation-name identifiers. This change
> tracks the occurrence of these strings in the wild to provide data
> on the impact dropping support for this would have.
> 
> BUG=423424
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=183856

TBR=timloh@chromium.org,dstockwell@chromium.org,alancutter@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=423424

Review URL: https://codereview.chromium.org/666433002

git-svn-id: svn://svn.chromium.org/blink/trunk@183877 bbb929c8-8fbe-4397-9dbb-9b2b20218538