Rename the new Ptr type to RawPtr to fix builds on Mac.

Ptr is already defined in MacTypes.h as a char* so it seems we
need to rename in order to avoid conflicts.

With these changes it is possible to change something simple
such as Range from RefCounted to RefCountedGarbageCollected
and have it work.

R=abarth@chromium.org, haraken@chromium.org
BUG=

Review URL: https://codereview.chromium.org/131503005

git-svn-id: svn://svn.chromium.org/blink/trunk@165889 bbb929c8-8fbe-4397-9dbb-9b2b20218538