CrOS GMC: Record pin/unpin metrics.

This CL adds pin/unpin metrics when user clicks pin/unpin button.

Bug: 1136254
Change-Id: I9bbbac6444cbbf2d74d74abbd8ec7d8b7ec31a4f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2462195
Commit-Queue: Jazz Xu <jazzhsu@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815484}

ash/system/media/media_tray.cc

@@ -162,6 +162,9 @@ MediaTray::PinButton::PinButton()
 void MediaTray::PinButton::ButtonPressed(views::Button* sender,
                                          const ui::Event& event) {
   MediaTray::SetPinnedToShelf(!MediaTray::IsPinnedToShelf());
+  base::UmaHistogramBoolean("Media.CrosGlobalMediaControls.PinAction",
+                            MediaTray::IsPinnedToShelf());
+
   SetImage(views::Button::STATE_NORMAL,
            CreateVectorIcon(
                MediaTray::IsPinnedToShelf() ? kPinnedIcon : kUnpinnedIcon,

tools/metrics/histograms/histograms_xml/media/histograms.xml

@@ -1239,6 +1239,15 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="Media.CrosGlobalMediaControls.PinAction" enum="BooleanPinned"
+    expires_after="2021-10-07">
+  <owner>jazzhsue@chromium.org</owner>
+  <owner>media-dev@chromium.org</owner>
+  <summary>
+    Record each time user pins/unpins CrOS global media controls.
+  </summary>
+</histogram>
+
 <histogram name="Media.CrosGlobalMediaControls.QuickSettingUserAction"
     enum="MediaSessionAction" expires_after="2021-10-07">
   <owner>jazzhsue@chromium.org</owner>