Confusing error message from dart2js on 'e || throw x'.

[lrhn]

Code like:
  (41 == 42) || throw "x";
gives an error saying:

Error: Expected an expression, but got 'throw'.
  41 == 42 || throw "not";
              ^^^^^

That makes it sound like "throw" is not an expression, where the problem is that it's not a LogicalAndExpression.

[floitschG]

cc @johnniwinther.
Removed Priority-Unassigned label.
Added Priority-Low label.

[askeksa-google]

Same issue as #24891 with a different operator.