Switch to enable the HMM transparent mode classifier

(cherry picked from commit 5c3ff6b)

Bug: chromium:1155071,webrtc:12265,chromium:1155477
Change-Id: I9d3119e9cbfdd5d7b41de2ed0f9dec92f7bf753d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/202258
Reviewed-by: Per Åhgren <[email protected]>
Commit-Queue: Gustaf Ullberg <[email protected]>
Cr-Original-Commit-Position: refs/heads/master@{#33037}
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/205280
Reviewed-by: Gustaf Ullberg <[email protected]>
Cr-Commit-Position: refs/branch-heads/4389@{open-webrtc-toolkit#5}
Cr-Branched-From: 7acc2d9-refs/heads/master@{#32986}

modules/audio_processing/aec3/transparent_mode.cc

@@ -23,10 +23,8 @@ bool DeactivateTransparentMode() {
   return field_trial::IsEnabled("WebRTC-Aec3TransparentModeKillSwitch");
 }
 
-bool DeactivateTransparentModeHmm() {
-  // HMM based classifier is temporarily disabled (https://crbug.com/1155071).
-  return true;
-  // return field_trial::IsEnabled("WebRTC-Aec3TransparentModeHmmKillSwitch");
+bool ActivateTransparentModeHmm() {
+  return field_trial::IsEnabled("WebRTC-Aec3TransparentModeHmm");
 }
 
 }  // namespace
@@ -232,10 +230,10 @@ std::unique_ptr<TransparentMode> TransparentMode::Create(
   if (config.ep_strength.bounded_erl || DeactivateTransparentMode()) {
     return nullptr;
   }
-  if (DeactivateTransparentModeHmm()) {
-    return std::make_unique<LegacyTransparentModeImpl>(config);
+  if (ActivateTransparentModeHmm()) {
+    return std::make_unique<TransparentModeImpl>();
   }
-  return std::make_unique<TransparentModeImpl>();
+  return std::make_unique<LegacyTransparentModeImpl>(config);
 }
 
 }  // namespace webrtc