Revert of Remove --ignition-staging to --ignition-osr implication. (patchset...

Revert of Remove --ignition-staging to --ignition-osr implication. (patchset #1 id:1 of https://codereview.chromium.org/2298613003/ )

Reason for revert:
Re-enable to get new data after recent changes.

Original issue's description:
> Remove --ignition-staging to --ignition-osr implication.
>
> Ignition OSR to turbofan seems to cause instruction selector crashes
> (where instructions selector gets simplified operators, probably
> because we break the effect chain somehow).
>
> BUG=chromium:641893
>
> Committed: https://crrev.com/26df3e230ebd8c7d1cd95ea54155959eee7cb830
> Cr-Commit-Position: refs/heads/master@{#39045}

TBR=bmeurer@chromium.org,jarin@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=chromium:641893

Review-Url: https://codereview.chromium.org/2318943002
Cr-Commit-Position: refs/heads/master@{#39231}

src/flag-definitions.h

@@ -299,6 +299,7 @@ DEFINE_BOOL(string_slices, true, "use string slices")
 DEFINE_BOOL(ignition, false, "use ignition interpreter")
 DEFINE_BOOL(ignition_staging, false, "use ignition with all staged features")
 DEFINE_IMPLICATION(ignition_staging, ignition)
+DEFINE_IMPLICATION(ignition_staging, ignition_osr)
 DEFINE_IMPLICATION(ignition_staging, turbo_from_bytecode)
 DEFINE_IMPLICATION(ignition_staging, ignition_preserve_bytecode)
 DEFINE_BOOL(ignition_eager, false, "eagerly compile and parse with ignition")