add UMA metrics for voice interaction entries.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index c9ff8801f5d904a9953c0192f36f97000e90d549..91ee84543e635e6e2808e947247775d81981f36c 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -25656,6 +25656,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Keyboard.Shortcuts.CrosMetaLayerEntryMetaShiftA">
+  <owner>muyuanli@chromium.org</owner>
+  <owner>zalcorn@chromium.org</owner>
+  <summary>
+    The number of times user starts meta layer through Meta + Shift + A.
+  </summary>
+</histogram>
+
 <histogram name="Keyboard.Shortcuts.CrosSearchKeyDelay" units="ms">
   <owner>xiaohuic@chromium.org</owner>
   <owner>zalcorn@chromium.org</owner>
@@ -25667,6 +25675,22 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Keyboard.Shortcuts.CrosVoiceInteractionEntryMetaA">
+  <owner>muyuanli@chromium.org</owner>
+  <owner>zalcorn@chromium.org</owner>
+  <summary>
+    The number of times user starts voice interaction through Meta + A.
+  </summary>
+</histogram>
+
+<histogram name="Keyboard.Shortcuts.CrosVoiceInteractionEntryMetaSpace">
+  <owner>muyuanli@chromium.org</owner>
+  <owner>zalcorn@chromium.org</owner>
+  <summary>
+    The number of times user starts voice interaction through Meta + Space.
+  </summary>
+</histogram>
+
 <histogram name="Kiosk.Launch.CryptohomeFailure" enum="LoginFailureReason">
   <owner>xiyuan@chromium.org</owner>
   <summary>Tracks cryptohome failure during kiosk launch.</summary>
@@ -68001,6 +68025,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Shelf.Shortcuts.CrosVoiceInteractionEntryAppListButtonLongPress">
+  <owner>muyuanli@chromium.org</owner>
+  <owner>zalcorn@chromium.org</owner>
+  <summary>
+    The number of times user starts voice interaction by long-pressing app list button.
+  </summary>
+</histogram>
+
 <histogram name="ShortcutsProvider.DatabaseSize">
   <owner>mpearson@chromium.org</owner>
   <summary>