Revert of Oilpan: Use weak pointers in StyleSheetContents caches.

Revert of Oilpan: Use weak pointers in StyleSheetContents caches. (https://codereview.chromium.org/185403016/)

Reason for revert:
This patch seems to have made a number of layout tests fail on the oilpan bots. Reverting while I investigate.

Original issue's description:
> Oilpan: Use weak pointers in StyleSheetContents caches.
> 
> This fixes use-after-free that could occur when StyleSheetContents
> dies when an allocation happens during insertion of a new
> StyleSheetContents. Using the built-in weak processing this will
> not happen because the iterator used during insertion will keep
> the StyleSheetContents alive.
> 
> R=erik.corry@gmail.com, haraken@chromium.org, vegorov@chromium.org
> NOTRY=true
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=168444

TBR=erik.corry@gmail.com,haraken@chromium.org,vegorov@chromium.org,zerny@chromium.org
NOTREECHECKS=true
NOTRY=true

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=168458

[Mads Ager (chromium), 2014-03-05 09:37:19]

Created Revert of Oilpan: Use weak pointers in StyleSheetContents caches.

[commit-bot: I haz the power, 2014-03-05 09:37:48]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ager@chromium.org/187473003/1

[commit-bot: I haz the power, 2014-03-05 09:38:37]

Change committed as 168458

[haraken, 2014-03-05 09:38:55]

lgtm

[Erik Corry, 2014-03-05 09:38:57]

lgtm

[haraken, 2014-03-05 09:38:57]

lgtm