Make the compact linked hash map, which is the default implementation for Map
(including map literals), a VM-internal class.
This makes it easy to have more efficient serialization of maps (although for
now, the implementation is straight-forward).
Refactor the compact hash class hierarchy to enable the VM-internal class and
the rest (also the Set classes) to share a maximal amount of code, by using
two different bases for implicit/explicit fields.
Remove existing proof-of-concept, C++-based internal VM-class.
BUG=http://dartbug.com/22982R=asiva@google.com
Review URL: https://codereview.chromium.org//1151523002
Daniel Andersson
ea46192ca3