[dart2wasm] Minor fixes for double string functions.
[dart2wasm] Minor fixes for double string functions.

Change-Id: Ia5165712ee8469699a7c9bf58b0fe86417b1b3d5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/265406
Commit-Queue: Ömer Ağacan <d15e39adaef0c3a64e4ea5d68f5c1b5be1f04e29@google.com>
Reviewed-by: Ömer Ağacan <d15e39adaef0c3a64e4ea5d68f5c1b5be1f04e29@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk