Assertion errors print poorly

[vsmenon]

The following code:

class JS {
  final String name;
  const JS([this.name]);
}

void main() {
  print(JS());
}

triggers this runtime error on the console:

Error: Assertion failed: file:///tmp/dartpadKBZCRA/main.dart:4:18

If break in the devtools debugger, it appears that:

(a) the entire error is:

Error: Assertion failed: file:///tmp/dartpadKBZCRA/main.dart:4:18
name != null
"A null value was passed into a non-nullable parameter name"

(b) there is code is dartpad that truncates everything but the first line:

              var msg = error.toString().split("\n")[0];
              console.log(msg);

[johnpryan]

I'm marking this as a duplicate of #1966, where we are tracking issues related to assertion error messages.