Revamp style resolver stats

Instead of the stats being behind a bunch of macros and needing to be enabled
at compile time we make them runtime enabled and expose them through
Internals.

With this new infrastructure you can do internals.setStyleResolverStatsEnabled(true) 
in a test and then trigger a recalc and finally call internals.styleResolverStatsTotalsReport()
to get a text dump of lots of interesting statistics. We can then land tests that dump
these statistics to track improvements or regressions in the matched property cache
or style sharing logic.

We might also consider adding a runtime flag to print out this information, or even making
it so that the web inspector could expose how much style sharing vs actual rule matching
a given page is doing.

Review URL: https://codereview.chromium.org/34623009

git-svn-id: svn://svn.chromium.org/blink/trunk@161894 bbb929c8-8fbe-4397-9dbb-9b2b20218538