[Nearby] Add metrics to track discovery counts and timing

For each discovery session, report the number of devices
  * discovered,
  * lost, and
  * present when a send starts.

Also, track the number of milliseconds between a the start of a
discovery session and
  * discovery of the first share target,
  * discovery of any share target, and
  * the start of a transfer.

Manually verified using chrome://histograms

Bug: 1105579
Change-Id: Ib998663d968fadcfb016c580ecf9119eefb5f0c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2530169Reviewed-by: James Vecore <vecore@google.com>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Commit-Queue: Ryan Hansberry <hansberry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827054}

chrome/browser/nearby_sharing/nearby_per_session_discovery_manager.cc

@@ -8,7 +8,6 @@
 
 #include "base/callback_helpers.h"
 #include "base/metrics/histogram_functions.h"
-#include "base/optional.h"
 #include "base/stl_util.h"
 #include "chrome/browser/nearby_sharing/attachment.h"
 #include "chrome/browser/nearby_sharing/logging/logging.h"
@@ -107,6 +106,10 @@ NearbyPerSessionDiscoveryManager::~NearbyPerSessionDiscoveryManager() {
   UnregisterSendSurface();
   base::UmaHistogramEnumeration(
       "Nearby.Share.Discovery.FurthestDiscoveryProgress", furthest_progress_);
+  base::UmaHistogramCounts100(
+      "Nearby.Share.Discovery.NumShareTargets.Discovered", num_discovered_);
+  base::UmaHistogramCounts100("Nearby.Share.Discovery.NumShareTargets.Lost",
+                              num_lost_);
 }
 
 void NearbyPerSessionDiscoveryManager::OnTransferUpdate(
@@ -142,8 +145,21 @@ void NearbyPerSessionDiscoveryManager::OnTransferUpdate(
 
 void NearbyPerSessionDiscoveryManager::OnShareTargetDiscovered(
     ShareTarget share_target) {
+  // Update metrics.
   UpdateFurthestDiscoveryProgressIfNecessary(
       DiscoveryProgress::kDiscoveredShareTargetNothingSent);
+  if (!base::Contains(discovered_share_targets_, share_target.id)) {
+    ++num_discovered_;
+    if (num_discovered_ == 1) {
+      base::UmaHistogramMediumTimes(
+          "Nearby.Share.Discovery.Delay.FromStartDiscoveryToFirstDiscovery",
+          base::TimeTicks::Now() - *discovery_start_time_);
+    }
+    base::UmaHistogramMediumTimes(
+        "Nearby.Share.Discovery.Delay.FromStartDiscoveryToAnyDiscovery",
+        base::TimeTicks::Now() - *discovery_start_time_);
+  }
+
   base::InsertOrAssign(discovered_share_targets_, share_target.id,
                        share_target);
   share_target_listener_->OnShareTargetDiscovered(share_target);
@@ -151,6 +167,9 @@ void NearbyPerSessionDiscoveryManager::OnShareTargetDiscovered(
 
 void NearbyPerSessionDiscoveryManager::OnShareTargetLost(
     ShareTarget share_target) {
+  if (base::Contains(discovered_share_targets_, share_target.id)) {
+    ++num_lost_;
+  }
   discovered_share_targets_.erase(share_target.id);
   share_target_listener_->OnShareTargetLost(share_target);
 }
@@ -158,6 +177,8 @@ void NearbyPerSessionDiscoveryManager::OnShareTargetLost(
 void NearbyPerSessionDiscoveryManager::StartDiscovery(
     mojo::PendingRemote<nearby_share::mojom::ShareTargetListener> listener,
     StartDiscoveryCallback callback) {
+  discovery_start_time_ = base::TimeTicks::Now();
+
   // Starting discovery again closes any previous discovery session.
   share_target_listener_.reset();
   share_target_listener_.Bind(std::move(listener));
@@ -216,6 +237,13 @@ void NearbyPerSessionDiscoveryManager::SelectShareTarget(
       transfer_update_listener_.BindNewPipeAndPassReceiver();
   transfer_update_listener_.reset_on_disconnect();
 
+  base::UmaHistogramCounts100(
+      "Nearby.Share.Discovery.NumShareTargets.PresentWhenSendStarts",
+      discovered_share_targets_.size());
+  base::UmaHistogramMediumTimes(
+      "Nearby.Share.Discovery.Delay.FromStartDiscoveryToStartSend",
+      base::TimeTicks::Now() - *discovery_start_time_);
+
   NearbySharingService::StatusCodes status =
       nearby_sharing_service_->SendAttachments(iter->second,
                                                std::move(attachments_));

chrome/browser/nearby_sharing/nearby_per_session_discovery_manager.h

@@ -10,6 +10,8 @@
 
 #include "base/containers/flat_map.h"
 #include "base/memory/weak_ptr.h"
+#include "base/optional.h"
+#include "base/time/time.h"
 #include "base/unguessable_token.h"
 #include "chrome/browser/nearby_sharing/attachment.h"
 #include "chrome/browser/nearby_sharing/nearby_sharing_service.h"
@@ -85,6 +87,15 @@ class NearbyPerSessionDiscoveryManager
   DiscoveryProgress furthest_progress_ =
       DiscoveryProgress::kDiscoveryNotAttempted;
 
+  // Used for metrics. Tracks the time when StartDiscovery() is called, or
+  // base::nullopt if never called.
+  base::Optional<base::TimeTicks> discovery_start_time_;
+
+  // Used for metrics. Tracks the total number devices discovered and lost in a
+  // given discovery session.
+  size_t num_discovered_ = 0;
+  size_t num_lost_ = 0;
+
   base::WeakPtrFactory<NearbyPerSessionDiscoveryManager> weak_ptr_factory_{
       this};
 };

tools/metrics/histograms/histograms_xml/others/histograms.xml

@@ -9227,6 +9227,21 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </token>
 </histogram>
 
+<histogram name="Nearby.Share.Discovery.Delay.FromStartDiscoveryTo{EndState}"
+    units="ms" expires_after="2021-08-19">
+  <owner>nohle@chromium.org</owner>
+  <owner>better-together-dev@google.com</owner>
+  <summary>
+    Records the delay between the start of the discovery session and {EndState}.
+  </summary>
+  <token key="EndState">
+    <variant name="AnyDiscovery" summary="the discovery of any share target"/>
+    <variant name="FirstDiscovery"
+        summary="the discovery of the first share target"/>
+    <variant name="StartSend" summary="the start of a transfer"/>
+  </token>
+</histogram>
+
 <histogram name="Nearby.Share.Discovery.FurthestDiscoveryProgress"
     enum="NearbyShareDiscoveryProgress" expires_after="2021-08-19">
   <owner>nohle@chromium.org</owner>
@@ -9249,6 +9264,21 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="Nearby.Share.Discovery.NumShareTargets.{Variation}"
+    units="share targets" expires_after="2021-08-19">
+  <owner>nohle@chromium.org</owner>
+  <owner>better-together-dev@google.com</owner>
+  <summary>
+    Records the number of share targets {Variation} in a single discovery
+    session. Emitted once during the discovery session.
+  </summary>
+  <token key="Variation">
+    <variant name="Discovered" summary="discovered"/>
+    <variant name="Lost" summary="lost"/>
+    <variant name="PresentWhenSendStarts" summary="present when a send starts"/>
+  </token>
+</histogram>
+
 <histogram name="Nearby.Share.Discovery.{Operation}"
     enum="NearbyShareServiceStatusCode" expires_after="2021-08-19">
   <owner>nohle@chromium.org</owner>