Translator: Fix dead-code-elimination corner case The DCE code had a corner case bug where a switch case containing multiple DCE'ed `break`s followed by another case would cause some of the DCE'ed statements in the first case to be doubly pruned, failing on an assertion. This was due to the fact that visitBlock() was asking traversal to continue if a new case was visited while pruning nodes, but the traversal does not take into account that some statements need to be skipped and so would also visit the pruned statements. If the pruned statements contain a branch instruction, they get re-pruned. The visitBlock() function that does the pruning is reworked so that it more clearly traverses the statements. Bug: chromium:1237200 Change-Id: Ib078c2ea73ade756c7d7ef5a5c489fa53c39f352 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3077659 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>