Add UMAs for video casting

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 6a1961d47885f08227f44d481fd0415d107e8a0c..161606f16a24e214a1d65c88d12304473a9b288e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -1194,6 +1194,42 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Cast.Sender.CastButtonShown">
+  <summary>
+    Records the number of times the cast button was shown to the user. The value
+    will be true if the button is enabled, and false if the button is disabled.
+    Note that depending on the current UX, it's possible that we hide the button
+    entirely if it's disabled, so it's possible for the false values to be 0.
+  </summary>
+</histogram>
+
+<histogram name="Cast.Sender.CastButtonShownInitialFullscreen">
+  <summary>
+    Records the number of times the cast button was shown to the user when the
+    video is fullscreened. The value will only be recorded once per fullscreen/
+    exit fullscreen session. The value will be true if the button is enabled,
+    and false if the button is disabled. Note that depending on the current UX,
+    it's possible that we hide the button entirely if it's disabled, so it's
+    possible for the false values to be 0.
+  </summary>
+</histogram>
+
+<histogram name="Cast.Sender.CastPlaySuccess">
+  <summary>
+    Records the result of a request to play remotely. The value will be true if
+    the playback succeeded, and false if there was an error.
+  </summary>
+</histogram>
+
+<histogram name="Cast.Sender.CastTimeRemainingPercentage"
+    units="percent remaining">
+  <summary>
+    Records the percentage of the video left by the time the remote playback is
+    stopped. This will be recorded when the playback is stopped by the user, or
+    when it's stopped by the cast device.
+  </summary>
+</histogram>
+
 <histogram name="Cellular.ActivationFailure">
   <summary>
     The count of cellular device activation failures (Chrome OS).