Revert "Disable --turbo-inline-array-builtins by default."

This reverts commit 32141e93.

Reason for revert: Got merged to stable end of last week.

Original change's description:
> Disable --turbo-inline-array-builtins by default.
> 
> Current chrome stable has a high number of crashes due to bugs in
> this feature. These bugs are already fixed but the fixes are hard
> to merge back. Therefore we decided to disable the feature in stable.
> This CL is intended to be merged to stable and then reverted in tot.
> 
> Bug: chromium:762020
> Change-Id: Ibd5a08e3b303a204fb84a408271a1c0f97cc5b7b
> Reviewed-on: https://chromium-review.googlesource.com/738176
> Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
> Commit-Queue: Georg Neis <neis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#48931}

TBR=jarin@chromium.org,neis@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: chromium:762020
Change-Id: Id1fe2f417e09a7b451484fc16710b09469cdb74d
Reviewed-on: https://chromium-review.googlesource.com/743321Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49025}

src/flag-definitions.h

@@ -434,7 +434,7 @@ DEFINE_VALUE_IMPLICATION(stress_inline, polymorphic_inlining, true)
 DEFINE_BOOL(trace_turbo_inlining, false, "trace TurboFan inlining")
 DEFINE_BOOL(inline_accessors, true, "inline JavaScript accessors")
 DEFINE_BOOL(inline_into_try, true, "inline into try blocks")
-DEFINE_BOOL(turbo_inline_array_builtins, false,
+DEFINE_BOOL(turbo_inline_array_builtins, true,
             "inline array builtins in TurboFan code")
 DEFINE_BOOL(use_osr, true, "use on-stack replacement")
 DEFINE_BOOL(trace_osr, false, "trace on-stack replacement")