Make sure that RawPtr<T> is stored in collections as an actual T pointer.

This is really important for performance. Compilers are not good at
automatically optimizing these simple pointer structures (especially
bad on 32 bit.)

This does it for RawPtr<T> which will fix our performance issues
non-oilpan. We should attempt to do this for Member<T> as well.
Collections of Member<T> pointers should use a raw T pointer
for storage as well. That is more challenging but will be
important for oilpan performance.

R=erik.corry@gmail.com, haraken@chromium.org, sigbjornf@opera.com
BUG=374431

Review URL: https://codereview.chromium.org/303463003

git-svn-id: svn://svn.chromium.org/blink/trunk@174867 bbb929c8-8fbe-4397-9dbb-9b2b20218538