compiler: change expression importing to use Import_expression

Change expression importing to use a new abstract interface class
Import_expression, so that we can more easily import expressions from
inlinable function bodies.  This is a refactoring with no affect on
compiler behavior.

Change-Id: I9178ad6b2272f9abad540576fcff72a746d1e5bc
Reviewed-by: Than McIntosh <>
Reviewed-by: Cherry Zhang <>
6 files changed