Add UMA histogram to evaluation changes to usbguard policy.

This will record if USB devices are attached before sign-in, after sign-in,
or at the lock screen, along with the device class.

Bug: 1011122
Change-Id: I83ad38b3d1fcb8e805de4014e81dda8c603d2d4c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1838526Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Nik Bhagat <nikunjb@chromium.org>
Commit-Queue: Allen Webb <allenwebb@google.com>
Cr-Commit-Position: refs/heads/master@{#705238}

tools/metrics/histograms/enums.xml

@@ -8060,6 +8060,12 @@ histogram as enum -->
 
 </enum>
 
+<enum name="ChromeOSUsbEventTiming">
+  <int value="0" label="kLoggedOut"/>
+  <int value="1" label="kLoggedIn"/>
+  <int value="2" label="kLocked"/>
+</enum>
+
 <enum name="ChromeOSUserImageId">
   <summary>
     Indices of the default images as defined in

tools/metrics/histograms/histograms.xml

@@ -20894,6 +20894,14 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram base="true" name="ChromeOS.USB.DeviceAttached"
+    enum="ChromeOSUsbEventTiming" expires_after="2020-10-01">
+  <owner>allenwebb@chromium.org</owner>
+  <owner>jorgelo@chromium.org</owner>
+  <owner>mnissler@chromium.org</owner>
+  <summary>Timing and number of USB devices attached.</summary>
+</histogram>
+
 <histogram name="ChromiumAndroidLinker.BrowserLoadTime" units="ms"
     expires_after="M99">
   <owner>rsesek@chromium.org</owner>
@@ -166021,6 +166029,39 @@ regressions. -->
   <affected-histogram name="ChromeOS.MachineIdRegen.AgeSeconds"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="ChromeOS.USBDeviceClass" separator=".">
+  <suffix name="App"
+      label="A device with only the application specific interface class."/>
+  <suffix name="Audio" label="An audio device."/>
+  <suffix name="AV" label="An audio/video device."/>
+  <suffix name="Card" label="A smart card reader."/>
+  <suffix name="Comm" label="A communication device."/>
+  <suffix name="Health" label="A personal healthcare device."/>
+  <suffix name="HID" label="A human-interface device."/>
+  <suffix name="Hub" label="A USB hub."/>
+  <suffix name="Image" label="A still image capture device."/>
+  <suffix name="Misc" label="A device with only the misc. interface class."/>
+  <suffix name="Other" label="All devices not covered by the other groups."/>
+  <suffix name="Phys" label="A physical device."/>
+  <suffix name="Print" label="A printer."/>
+  <suffix name="Sec" label="A security device (e.g. fingerprint reader)."/>
+  <suffix name="Storage" label="A storage device."/>
+  <suffix name="Vendor"
+      label="A device with only the vendor specific interface class."/>
+  <suffix name="Video" label="A video device."/>
+  <suffix name="Wireless" label="A wireless controller device."/>
+  <affected-histogram name="ChromeOS.USB.DeviceAttached.Recognized"/>
+  <affected-histogram name="ChromeOS.USB.DeviceAttached.Unrecognized"/>
+</histogram_suffixes>
+
+<histogram_suffixes name="ChromeOS.USBDeviceRecognized" separator=".">
+  <suffix base="true" name="Recognized"
+      label="A device that was already added to the list of trusted devices."/>
+  <suffix base="true" name="Unrecognized"
+      label="A device that was not in the list of trusted devices yet."/>
+  <affected-histogram name="ChromeOS.USB.DeviceAttached"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="Clients.StaleWhileRevalidateExperiment" separator="."
     ordering="prefix">
   <suffix name="Clients.StaleWhileRevalidateExperiment"