Turn the setup of the oilpan heap infrastructure on by default.

In order to be able to ship certain simple modules using the heap
infrastructure we need the infrastructure to be turned on by default.
That way, ENABLE(OILPAN) controls only which parts of Blink are
shipped with the objects in the traced heap.

BUG=

Review URL: https://codereview.chromium.org/142483004

git-svn-id: svn://svn.chromium.org/blink/trunk@165896 bbb929c8-8fbe-4397-9dbb-9b2b20218538