scanning: Create histogram for ready time

The histogram records the time between sending a request for scanners
and receiving capabilities for the selected scanner (i.e. the time that
passes before being able to perform a scan).

Bug: 1059779
Change-Id: I8be9453945054848d1b534bf43ba29e2653731da
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2597656Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Reviewed-by: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Jesse Schettler <jschettler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841078}

chrome/browser/chromeos/scanning/scan_service.cc

@@ -245,6 +245,7 @@ ScanService::ScanService(LorgnetteScannerManager* lorgnette_scanner_manager,
 ScanService::~ScanService() = default;
 
 void ScanService::GetScanners(GetScannersCallback callback) {
+  get_scanners_time_ = base::TimeTicks::Now();
   lorgnette_scanner_manager_->GetScannerNames(
       base::BindOnce(&ScanService::OnScannerNamesReceived,
                      weak_ptr_factory_.GetWeakPtr(), std::move(callback)));
@@ -351,6 +352,18 @@ void ScanService::OnScannerCapabilitiesReceived(
     return;
   }
 
+  // If this is the first time capabilities have been received since the last
+  // call to GetScanners(), record the time between the two events to capture
+  // the time between the Scan app launching and the user being able to interact
+  // with the app (e.g. select a scanner, change scan settings, or start a
+  // scan). If the user selects a different scanner and new capabilities are
+  // received, don't record the metric again.
+  if (!get_scanners_time_.is_null()) {
+    base::UmaHistogramMediumTimes("Scanning.ReadyTime",
+                                  base::TimeTicks::Now() - get_scanners_time_);
+    get_scanners_time_ = base::TimeTicks();
+  }
+
   std::move(callback).Run(
       mojo::ConvertTo<mojo_ipc::ScannerCapabilitiesPtr>(capabilities.value()));
 }

chrome/browser/chromeos/scanning/scan_service.h

@@ -157,6 +157,10 @@ class ScanService : public scanning::mojom::ScanService, public KeyedService {
   // Tracks the number of pages scanned for histogram recording.
   int num_pages_scanned_;
 
+  // The time at which GetScanners() is called. Used to record the time between
+  // a user launching the Scan app and being able to interact with it.
+  base::TimeTicks get_scanners_time_;
+
   base::WeakPtrFactory<ScanService> weak_ptr_factory_{this};
 };
 

tools/metrics/histograms/histograms_xml/scanning/histograms.xml

@@ -40,6 +40,18 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   <summary>Records the number of pages scanned in a successful scan.</summary>
 </histogram>
 
+<histogram name="Scanning.ReadyTime" units="ms" expires_after="2021-12-04">
+  <owner>gavinwill@chromium.org</owner>
+  <owner>jschettler@chromium.org</owner>
+  <owner>cros-peripherals@google.com</owner>
+  <summary>
+    Records the time between sending a request for scanners and receiving
+    capabilities for the selected scanner, which is essentially the time between
+    the user launching the Scan app and being able to interact with it to select
+    a scanner, change scan settings, or start a scan.
+  </summary>
+</histogram>
+
 <histogram name="Scanning.ScanAppEntryPoint" enum="ScanAppEntryPoint"
     expires_after="2021-12-04">
   <owner>gavinwill@chromium.org</owner>