Split module optimization back into two parts.

When rehydration was deleted (http://review.skia.org/585398), the two
functions `eliminate_dead_code_from_loaded_module` and
`Compiler::optimizeModuleAfterLoading` were combined. This CL splits
them back apart; the dead-code elimination function is now a public
method called `optimizeModuleBeforeMinifying` and is only called by
the minifier.

Sorry for the churn!

Change-Id: Iecdacd2541e08d897f952f455b31fcbf6e67bbda
Bug: skia:13775
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/586278
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
3 files changed