Use a feature instead of switch for dictation listening.

With this change, you can enable experimental dictation listening
behavior (continuous dictation, longer listening and allow profanity)
using the command line flag:
--enable-features="ExperimentalAccessibilityDictationListening".

This will make rollout easier.

Bug: 1200667
Change-Id: I95e154e69b6da90a18a531e52c6ba50357d4929a
AX-Relnotes: N/A
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2872553
Commit-Queue: Katie Dektar <katie@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#879540}
NOKEYCHECK=True
GitOrigin-RevId: 90a3cf3f80daeacd2e929155d58ab9222137f499
diff --git a/metrics/histograms/enums.xml b/metrics/histograms/enums.xml
index 7dead19..b4dd0d4 100644
--- a/metrics/histograms/enums.xml
+++ b/metrics/histograms/enums.xml
@@ -44731,6 +44731,8 @@
   <int value="-1772942854" label="LongPressBackForHistory:enabled"/>
   <int value="-1772905637"
       label="RunVideoCaptureServiceInBrowserProcess:enabled"/>
+  <int value="-1772476751"
+      label="ExperimentalAccessibilityDictationListening:enabled"/>
   <int value="-1772172557" label="enable-osk-overscroll"/>
   <int value="-1771552112" label="QueryTilesInOmnibox:disabled"/>
   <int value="-1768672408" label="ChromeDuplex:disabled"/>
@@ -47475,6 +47477,8 @@
   <int value="630308195" label="SignInProfileCreation:enabled"/>
   <int value="630776247" label="USBGuard:disabled"/>
   <int value="630947363" label="touch-events"/>
+  <int value="632324382"
+      label="ExperimentalAccessibilityDictationListening:disabled"/>
   <int value="632340413" label="network-settings-config"/>
   <int value="633442161" label="ExperimentalUi:disabled"/>
   <int value="634789085" label="LayeredAPI:disabled"/>