Revert "Replace style sharing cousin list search with LRU"

This reverts commit ed002c01e93c3d9ee90fdf16d7461b149176c650.

Landing this as a speculative fix for the three perf regressions from
the listed bug.

TBR=ojan
BUG=286376

Review URL: https://chromiumcodereview.appspot.com/23701014

git-svn-id: svn://svn.chromium.org/blink/trunk@157383 bbb929c8-8fbe-4397-9dbb-9b2b20218538