Further improve type optimization reusing the type argument vector of the

Further improve type optimization reusing the type argument vector of the
instantiator of generic objects (fixes issue 10149).
This optimization considers the generic type argument vector of the instance
being allocated as well as the generic type argument vector of the compile
time type of the instantiator.
If the instance vector is a prefix of the instantiator vector, the instantiator
vector can be shared by the new instance.

R=srdjan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=22155

[srdjan, 2013-04-29 23:38:55]

lgtm

[regis, 2013-04-29 23:39:52]

Committed patchset #1 manually as r22155 (presubmit successful).