RFR: 8267317: Remove DeferredTypeCompleter [v2]

[Vicente Romero]

On Tue, 18 May 2021 13:08:05 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> This pathc removes DeferredTypeCompleter, which seems like a dubious abstraction. In its place there is now a `complete` method on `DeferredType` which is overridden by `ArgumentType`. The only problematic usage is from `StructuralStuckChecker`, but after inspecting the code I realized that the only side effect this code expected from calling `DeferredType::check` was to set the deferred type mode to `SPECULATIVE`, which we can easily do inline.
>
> Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove redundant assigment of DeferredType::mode

lgtm

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Marked as reviewed by vromero (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/4091