Improve WTF::HashTable performance by changing probing method

Our current HashTable implementation uses a linear probing system where
the delta is a hash of the given hash, which for integers requires
numerous shift and add operations to compute. This patch takes some
inspiration from CPython's dict implementation[1] to improve average
performance.

The new probing system is based off CPython's implementation -- we use a
linear congruential generator (x <- x*5+1), but for the first few probes
we also mix in the original hash (we shift this right by 5 each probe,
so we should use all the bits of the hash if the hash table is at least
32 objects big).

[1] http://svn.python.org/projects/python/trunk/Objects/dictobject.c

BUG=

Review URL: https://chromiumcodereview.appspot.com/17583004

git-svn-id: svn://svn.chromium.org/blink/trunk@153057 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Creating a mediastream watchlist entry
And adding myself to it.

NOTRY=True
BUG=

Review URL: https://chromiumcodereview.appspot.com/17856002

git-svn-id: svn://svn.chromium.org/blink/trunk@153058 bbb929c8-8fbe-4397-9dbb-9b2b20218538