Reland "Enable ArcPreImeKeyEventSupport by default."

This is a reland of e73788df
The original change was reverted due to the input lag. The root cause
was fixed in Android side.
Please also refer to go/cros-postmortem-input-lag

Original change's description:
> Enable ArcPreImeKeyEventSupport by default.
>
> Bug: b:148193316
> Test: tast run arc.PreImeKeyEvent
> Change-Id: I8ba1437e5a94f3a251d9a7e658df2d995ddd3dec
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2391184
> Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
> Commit-Queue: Yuichiro Hanada <yhanada@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#804664}

Bug: b:148193316, b:174430314, chromium:1153410
Change-Id: Ic23006790fd4d5a26324acf4263616a55f383e74
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2599683
Commit-Queue: Yuichiro Hanada <yhanada@chromium.org>
Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#842276}

chromeos/constants/chromeos_features.cc

@@ -88,8 +88,8 @@ const base::Feature kArcManagedAdbSideloadingSupport{
     "ArcManagedAdbSideloadingSupport", base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Controls whether to enable support for View.onKeyPreIme() of ARC apps.
-const base::Feature kArcPreImeKeyEventSupport{
-    "ArcPreImeKeyEventSupport", base::FEATURE_DISABLED_BY_DEFAULT};
+const base::Feature kArcPreImeKeyEventSupport{"ArcPreImeKeyEventSupport",
+                                              base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Enables or disables auto screen-brightness adjustment when ambient light
 // changes.