Create a class for evaluating const instance creation expressions.

Create a class for evaluating const instance creation expressions.

Previously the methods for evaluating const instance creation
expressions were all in the ConstantValueComputer class.  Moving them
to their own class allows for the possibility of evaluating them in
the ConstantVisitor, which in a future CL should allow us to avoid
making these expressions part of the const dependency graph.

R=brianwilkerson@google.com

Committed: https://code.google.com/p/dart/source/detail?r=45533

[Paul Berry, 2015-05-05 16:30:31]

paulberry@google.com changed reviewers:
+ brianwilkerson@google.com, scheglov@google.com

[Paul Berry, 2015-05-05 16:30:32]

Mostly this is just code motion.  The diffs make this look like a much larger
change than it is.

[Brian Wilkerson, 2015-05-05 17:35:31]

LGTM

[Paul Berry, 2015-05-05 17:47:46]

Committed patchset #1 (id:1) manually as 45533 (presubmit successful).