[interpreter] Preserve bytecode by default.

This enables preservation of bytecode by default. Thus far bytecode was
cleared during tier-up by default and was only preserved in the staging
configuration.

R=rmcilroy@chromium.org

Review-Url: https://codereview.chromium.org/2384063010
Cr-Commit-Position: refs/heads/master@{#40158}

src/flag-definitions.h

@@ -295,7 +295,6 @@ 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, ignition_preserve_bytecode)
 DEFINE_BOOL(ignition_eager, false, "eagerly compile and parse with ignition")
 DEFINE_STRING(ignition_filter, "*", "filter for ignition interpreter")
 DEFINE_BOOL(ignition_deadcode, true,
@@ -305,7 +304,7 @@ DEFINE_BOOL(ignition_peephole, true, "use ignition peephole optimizer")
 DEFINE_BOOL(ignition_reo, true, "use ignition register equivalence optimizer")
 DEFINE_BOOL(ignition_filter_expression_positions, true,
             "filter expression positions before the bytecode pipeline")
-DEFINE_BOOL(ignition_preserve_bytecode, false,
+DEFINE_BOOL(ignition_preserve_bytecode, true,
             "preserve generated bytecode even when switching tiers")
 DEFINE_BOOL(print_bytecode, false,
             "print bytecode generated by ignition interpreter")