[WebRTC] Make ThermalResource ENABLED_BY_DEFAULT.

This feature has now rolled out to stable, so we change the default of
the feature to enabled, allowing us to remove the .gcl file when M87 is
promoted to Stable.

Because serious/critical thermal signals are so rare (<1% of macOS
population) and the impact of this resource is little-to-none, an
alternative would be to simply delete the ThermalResource.

However, by keeping the code, if the macOS signal is improved in a
future release or if the thermal resource becomes available on more
platforms (there are WIP CLs on Android and ChromeOS) then having the
ThermalResource will automatically make use of these signals. And by
having the base::Feature still in here, if changes to OS signals were
to cause any regressions, we can use it as a kill-switch.

// TBR in place of Evan's +1 (he's not a committer yet).
TBR=guidou@chromium.org

Bug: chromium:1100336
Change-Id: I03a2a765bd4b8cbbca5a9b618c71d7214b830ce6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2418335Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808843}

third_party/blink/renderer/modules/peerconnection/rtc_peer_connection_handler_test.cc

@@ -1286,11 +1286,24 @@ TEST_F(RTCPeerConnectionHandlerTest, CheckInsertableStreamsConfig) {
   }
 }
 
-TEST_F(RTCPeerConnectionHandlerTest, ThermalResourceIsDisabledByDefault) {
+TEST_F(RTCPeerConnectionHandlerTest, ThermalResourceIsEnabledByDefault) {
   EXPECT_TRUE(mock_peer_connection_->adaptation_resources().IsEmpty());
   pc_handler_->OnThermalStateChange(
       base::PowerObserver::DeviceThermalState::kCritical);
-  // A ThermalResource is not created despite the thermal signal.
+  // A ThermalResource is created in response to the thermal signal.
+  EXPECT_FALSE(mock_peer_connection_->adaptation_resources().IsEmpty());
+}
+
+TEST_F(RTCPeerConnectionHandlerTest,
+       ThermalStateChangeDoesNothingIfThermalResourceIsDisabled) {
+  // Overwrite base::Feature kWebRtcThermalResource's default to DISABLED.
+  base::test::ScopedFeatureList scoped_feature_list;
+  scoped_feature_list.InitAndDisableFeature(kWebRtcThermalResource);
+
+  EXPECT_TRUE(mock_peer_connection_->adaptation_resources().IsEmpty());
+  pc_handler_->OnThermalStateChange(
+      base::PowerObserver::DeviceThermalState::kCritical);
+  // A ThermalResource is created in response to the thermal signal.
   EXPECT_TRUE(mock_peer_connection_->adaptation_resources().IsEmpty());
 }
 

third_party/blink/renderer/modules/peerconnection/thermal_resource.cc

@@ -15,7 +15,7 @@ const int kReportIntervalSeconds = 10;
 }  // namespace
 
 const base::Feature kWebRtcThermalResource{"WebRtcThermalResource",
-                                           base::FEATURE_DISABLED_BY_DEFAULT};
+                                           base::FEATURE_ENABLED_BY_DEFAULT};
 
 // static
 scoped_refptr<ThermalResource> ThermalResource::Create(