camera: Record client type during OpenDevice()

Add entry to record the client type during OpenDevice(). This allows to
determine the number of Chrome, Android camera users respectively. The
client side CL is at crrev.com/c/2619449

  2. emerge and deploy cros-camera
  3. Verify that the metric is logged in chrome://histograms

Bug: b/176787333
Test: 1. Build and deploy simple chrome.
Change-Id: I8159eae088b83a99dba5657e04ac63e965d01f20
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2621452Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Wei Lee <wtlee@chromium.org>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Commit-Queue: Jasmine Chen <lnishan@google.com>
Cr-Commit-Position: refs/heads/master@{#842876}

tools/metrics/histograms/enums.xml

@@ -9941,6 +9941,16 @@ histogram as enum -->
   <int value="2" label="First service disabled"/>
 </enum>
 
+<enum name="ChromeOSCameraClientType">
+  <int value="0" label="Unknown"/>
+  <int value="1" label="Testing"/>
+  <int value="2" label="Chrome"/>
+  <int value="3" label="Android"/>
+  <int value="4" label="PluginVM"/>
+  <int value="5" label="AshChrome"/>
+  <int value="6" label="LacrosChrome"/>
+</enum>
+
 <enum name="ChromeOSCameraErrorType">
   <int value="1" label="Device"/>
   <int value="2" label="Request"/>

tools/metrics/histograms/histograms_xml/chromeos/histograms.xml

@@ -181,6 +181,16 @@ incoming reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="ChromeOS.Camera.OpenDeviceClientType"
+    enum="ChromeOSCameraClientType" expires_after="2021-05-16">
+  <owner>lnishan@chromium.org</owner>
+  <owner>chromeos-camera-eng@google.com</owner>
+  <summary>
+    Records which client type (e.g., Chrome, Android) is opening a camera
+    device.
+  </summary>
+</histogram>
+
 <histogram name="ChromeOS.Camera.OpenDeviceLatency" units="microseconds"
     expires_after="2021-05-16">
   <owner>wtlee@chromium.org</owner>