Unflag the stats selection algorithm.

This ships:
- RTCPeerConnection.getStats(optional MediaStreamTrack? selector = null)
- RTCRtpSender.getStats()
- RTCRtpReceiver.getStats()

Spec:
https://w3c.github.io/webrtc-pc/#dfn-stats-selection-algorithm

Design doc:
https://docs.google.com/document/d/18BywbtXgHCjsbR5nWBedpzqDjAfXrFSTJNiADnzoK0w/edit?usp=sharing

Intent to Ship:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/2mGY257k4-M

Bug: 680172
Change-Id: I63c7991270489434cf67c9ebf7794a2648ceb6b8
Reviewed-on: https://chromium-review.googlesource.com/997554
Commit-Queue: Henrik Boström <hbos@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549201}

third_party/WebKit/LayoutTests/virtual/stable/webexposed/global-interface-listing-expected.txt

@@ -4691,11 +4691,13 @@ interface RTCRtpReceiver
     getter track
     method constructor
     method getContributingSources
+    method getStats
 interface RTCRtpSender
     attribute @@toStringTag
     getter dtmf
     getter track
     method constructor
+    method getStats
     method replaceTrack
 interface RTCSessionDescription
     attribute @@toStringTag

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

@@ -1295,33 +1295,25 @@ ScriptPromise RTCPeerConnection::getStats(
   if (argument->IsUndefined())
     return PromiseBasedGetStats(script_state, nullptr);
   auto isolate = callback_or_selector.GetIsolate();
-  // Default type error message, as it would have been generated by V8 bindings.
-  const char* type_error_message =
-      "The callback provided as parameter 1 is not a function.";
   // Custom binding for spec-compliant "getStats(MediaStreamTrack? selector)".
-  if (RuntimeEnabledFeatures::RTCPeerConnectionGetStatsSelectorEnabled()) {
-    // null is a valid selector value, but value of wrong type isn't. |selector|
-    // set to no value means type error.
-    base::Optional<MediaStreamTrack*> selector;
-    if (argument->IsNull()) {
-      selector = base::Optional<MediaStreamTrack*>(nullptr);
-    } else {
-      MediaStreamTrack* track =
-          V8MediaStreamTrack::ToImplWithTypeCheck(isolate, argument);
-      if (track)
-        selector = base::Optional<MediaStreamTrack*>(track);
-    }
-    if (selector.has_value())
-      return PromiseBasedGetStats(script_state, *selector);
-    // Override type error message to reflect that a selector is also a valid
-    // argument.
-    type_error_message =
-        "The argument provided as parameter 1 is neither a callback (function) "
-        "or selector (MediaStreamTrack or null).";
+  // null is a valid selector value, but value of wrong type isn't. |selector|
+  // set to no value means type error.
+  base::Optional<MediaStreamTrack*> selector;
+  if (argument->IsNull()) {
+    selector = base::Optional<MediaStreamTrack*>(nullptr);
+  } else {
+    MediaStreamTrack* track =
+        V8MediaStreamTrack::ToImplWithTypeCheck(isolate, argument);
+    if (track)
+      selector = base::Optional<MediaStreamTrack*>(track);
   }
+  if (selector.has_value())
+    return PromiseBasedGetStats(script_state, *selector);
   ExceptionState exception_state(isolate, ExceptionState::kExecutionContext,
                                  "RTCPeerConnection", "getStats");
-  exception_state.ThrowTypeError(type_error_message);
+  exception_state.ThrowTypeError(
+      "The argument provided as parameter 1 is neither a callback (function) "
+      "or selector (MediaStreamTrack or null).");
   return exception_state.Reject(script_state);
 }
 

third_party/blink/renderer/modules/peerconnection/rtc_peer_connection.idl

@@ -126,9 +126,6 @@ enum RTCIceConnectionState {
     //    List of implemented stats:
     //    https://cs.chromium.org/chromium/src/third_party/webrtc/api/stats/rtcstats_objects.h
     //    See also RTCRtpSender.getStats() and RTCRtpReceiver.getStats().
-    //
-    //    Note: The version of 2) that takes a |selector| is behind flag
-    //    RuntimeEnabled=RTCPeerConnectionGetStatsSelector.
     [CallWith=ScriptState] Promise<any> getStats(optional any callbackOrSelector);
 
     // RTP Media API

third_party/blink/renderer/modules/peerconnection/rtc_rtp_receiver.idl

@@ -7,6 +7,6 @@
 interface RTCRtpReceiver {
     readonly attribute MediaStreamTrack track;
     sequence<RTCRtpContributingSource> getContributingSources();
-    [RuntimeEnabled=RTCPeerConnectionGetStatsSelector, CallWith=ScriptState] Promise<RTCStatsReport> getStats();
+    [CallWith=ScriptState] Promise<RTCStatsReport> getStats();
     // TODO(hbos): Support every member of the spec. https://crbug.com/700916
 };

third_party/blink/renderer/modules/peerconnection/rtc_rtp_sender.idl

@@ -10,6 +10,6 @@ interface RTCRtpSender {
     [RuntimeEnabled=RTCRtpSenderParameters] RTCRtpParameters getParameters();
     [Measure, CallWith=ScriptState] Promise<void> replaceTrack(MediaStreamTrack? withTrack);
     [Measure] readonly attribute RTCDTMFSender? dtmf;
-    [RuntimeEnabled=RTCPeerConnectionGetStatsSelector, CallWith=ScriptState] Promise<RTCStatsReport> getStats();
+    [CallWith=ScriptState] Promise<RTCStatsReport> getStats();
     // TODO(hbos): Implement the rest of RTCRtpSender, https://crbug.com/700916.
 };

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -1011,10 +1011,6 @@
       name: "RootLayerScrolling",
       status: "stable",
     },
-    {
-      name: "RTCPeerConnectionGetStatsSelector",
-      status: "experimental",
-    },
     {
       name: "RtcPeerConnectionId",
       origin_trial_feature_name: "RtcPeerConnectionId",