Revert of Get rid of the StyleResolver throwaway timer. (https://codereview.chromium.org/139153013/)

Reason for revert:
Suspected to be the culprit for lots of crashes on canary

Original issue's description:
> Get rid of the StyleResolver throwaway timer.
> 
> Since we moved RuleSets to live off StyleSheetContents, this memory
> optimization really doesn't buy us anything. In the future, we might
> want to consider clearing the RuleSets of the StyleSheetContents,
> but in the meantime, we don't need this code.
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=165355

TBR=esprehn@chromium.org,eseidel@chromium.org,ojan@chromium.org
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/139013007

git-svn-id: svn://svn.chromium.org/blink/trunk@165390 bbb929c8-8fbe-4397-9dbb-9b2b20218538