Implement static const variables

[sethladd]

New language feature.

A constant expression is an expression whose value can never change, and that can be evaluated entirely at compile time. A constant expression is one of the following:

A reference to a constant variable.

A constant variable is a variable whose declaration includes the modifier const. A constant variable is always implicitly final. A constant variable must be initialized to a compile-time constant or a compile-time error occurs.
Constant variables are not yet implemented.

See also http://www.dartlang.org/docs/spec/latest/dart-language-specification.html

[sethladd]

Added Triaged label.

[sethladd]

Marked this as being blocked by #3395.

[anders-sandholm]

Added Area-Language label.
Unmarked this as being blocked by #3395, #2505, #3323.

[anders-sandholm]

Closing as this is implemented in the spec.
Tracking implementation progress in issue #2505, issue #3395 and issue #3323.

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Added Done label.

[anders-sandholm]

Added Duplicate label.
Marked as being merged into #3549.

[DartBot]

This comment was originally written by amouravski@google.com

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Removed Type-Meta label.
Added Type-Enhancement label.