[CrOS PhoneHub] Update MultiDevice.SecureChannel.Nearby.ConnectionMedium

This metric records one bucket when a connection is accepted and another
bucket when a WebRTC upgrade occurs, as a measure of the effectiveness
of WebRTC upgrades. If these buckets have equal counts, this means that
WebRTC upgrades occurred 100% of the time.

However, WebRTC upgrades are not instantaneous; the median upgrade time
is ~5s, and the 95th percentile is 30s. For short-lived connections, we
don't provide enough time for the connection to upgrade, so this
shouldn't really be counted as a "failure" to upgrade.

If a connection disconnects in under 30s, we now log to a new bucket
indicating that the connection disconnected before 30s was up. This will
help us measure a more accurate success rate for WebRTC upgrades.

Bug: 1163779, 1106937
Change-Id: I135820c6541e96818cced0e91719a591ec1510d0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2617304
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841695}

chrome/browser/chromeos/secure_channel/nearby_connection_broker_impl.cc

@@ -33,12 +33,19 @@ NearbyConnectionBrokerImpl::Factory* g_test_factory = nullptr;
 constexpr base::TimeDelta kConnectionStatusChangeTimeout =
     base::TimeDelta::FromSeconds(10);
 
+// The amount of time by which we can expect a WebRTC upgrade to have been
+// completed. According to metrics, 30 seconds is the 95th+ percentile of how
+// long it takes to upgrade to WebRTC.
+constexpr base::TimeDelta kWebRtcUpgradeDelay =
+    base::TimeDelta::FromSeconds(30);
+
 // Numerical values should not be reused or changed since this is used by
 // metrics.
 enum class ConnectionMedium {
   kConnectedViaBluetooth = 0,
   kUpgradedToWebRtc = 1,
-  kMaxValue = kUpgradedToWebRtc
+  kDisconnectedInUnder30Seconds = 2,
+  kMaxValue = kDisconnectedInUnder30Seconds
 };
 
 void RecordConnectionMediumMetric(ConnectionMedium medium) {
@@ -151,6 +158,15 @@ void NearbyConnectionBrokerImpl::Disconnect(
     util::RecordNearbyDisconnection(reason);
   }
 
+  if (!has_recorded_no_webrtc_metric_ && !has_upgraded_to_webrtc_ &&
+      !time_when_connection_accepted_.is_null() &&
+      (base::Time::Now() - time_when_connection_accepted_) <
+          kWebRtcUpgradeDelay) {
+    has_recorded_no_webrtc_metric_ = true;
+    RecordConnectionMediumMetric(
+        ConnectionMedium::kDisconnectedInUnder30Seconds);
+  }
+
   if (!need_to_disconnect_endpoint_) {
     TransitionToDisconnectedAndInvokeCallback();
     return;
@@ -398,6 +414,7 @@ void NearbyConnectionBrokerImpl::OnBandwidthChanged(
   PA_LOG(INFO) << "Bandwidth changed: " << medium;
 
   if (medium == Medium::kWebRtc) {
+    has_upgraded_to_webrtc_ = true;
     RecordConnectionMediumMetric(ConnectionMedium::kUpgradedToWebRtc);
 
     DCHECK(!time_when_connection_accepted_.is_null());

chrome/browser/chromeos/secure_channel/nearby_connection_broker_impl.h

@@ -168,6 +168,14 @@ class NearbyConnectionBrokerImpl
   // Starts empty, then set in OnEndpointDiscovered().
   std::string remote_endpoint_id_;
 
+  // Starts as false and changes to true when WebRTC upgrade occurs.
+  bool has_upgraded_to_webrtc_ = false;
+
+  // Whether or not a metric has been logged to note that a metric has been
+  // logged indicated that Disconnect() was called before a WebRTC upgrade
+  // occurred.
+  bool has_recorded_no_webrtc_metric_ = false;
+
   // Starts as false; set to true in OnConnectionInitiated() and back to false
   // in OnDisconnected().
   bool need_to_disconnect_endpoint_ = false;

tools/metrics/histograms/enums.xml

@@ -66900,6 +66900,9 @@ https://www.dmtf.org/sites/default/files/standards/documents/DSP0134_2.7.1.pdf
 <enum name="SecureChannelNearbyConnectionMedium">
   <int value="0" label="Connected via Bluetooth"/>
   <int value="1" label="Upgraded bandwidth to WebRTC"/>
+  <int value="2"
+      label="Disconnected in under 30s without WebRTC upgrade; not provided
+             enough time to complete bandwidth upgrade process"/>
 </enum>
 
 <enum name="SecureCookieAction">