Argument type checks could use receiver to get instantiator type
arguments. Receiver could be captured and allocated in a context.
So initial context should be allocated before doing argument type
checks.
This CL also removes useless storing of uninitialized (null) context into
'parent' when allocating initial context.
Change-Id: Iec41f1bd474ba8cfccc360b96b3461fe760edddb
Reviewed-on: https://dart-review.googlesource.com/62706
Reviewed-by: Zach Anderson <zra@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>