Check field type when evaluating initializing formals.

Check field type when evaluating initializing formals.

This performs proper type checking when the type of a field differs
from the type of a field formal parameter, e.g.:

  class A {
    final T1 x;
    const A(T2 this.x);
  }

  // only works if <expr> is a subtype of both T1 and T2.
  var a = const A(<expr>);

Previously we only checked the parameter type (T2 in the above example).

BUG=dartbug.com/16391
R=brianwilkerson@google.com

Committed: https://code.google.com/p/dart/source/detail?r=41048

[Paul Berry, 2014-10-10 18:20:22]

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

[Brian Wilkerson, 2014-10-10 18:32:17]

LGTM

[Paul Berry, 2014-10-10 18:50:24]

Committed patchset #1 (id:1) manually as 41048 (presubmit successful).