Revert of use ForceSet instead of Set when setting properties with attributes (https://codereview.chromium.org/373033002/)

Reason for revert:
I'm reverting this CL because the description doesn't explain why the change was made and there's no test.

Original issue's description:
> use ForceSet instead of Set when setting properties with attributes
> 
> R=jochen@chromium.org
> 
> BUG=
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=177659

TBR=jochen@chromium.org,dcarney@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/379533004

git-svn-id: svn://svn.chromium.org/blink/trunk@177679 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove WebWorkerInfo as it doesn't have any users.

BUG=

Review URL: https://codereview.chromium.org/374053004

git-svn-id: svn://svn.chromium.org/blink/trunk@177680 bbb929c8-8fbe-4397-9dbb-9b2b20218538