Define a few simple UMA metrics for the component updater.

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 87051080d7ba4c8c09251e4b3b28eac4f62c4ecf..b4966d11b443dd8d5cd78c60c9033f7a2a7174ad 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -5138,6 +5138,35 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Number of tries before successful ping. 99 means giving up.</summary>
 </histogram>
 
+<histogram name="ComponentUpdater.Install.Count">
+  <owner>sorin@chromium.org</owner>
+  <summary>
+    The number of times the component updater called UpdateClient::Install. This
+    corresponds to the number of manual component update checks done performed
+    as a result of a user action.
+  </summary>
+</histogram>
+
+<histogram name="ComponentUpdater.Update.Count">

[Ilya Sherman, 2016/03/09 02:28:00]

Would it make sense to combine the install and update counts in a single
enumerated histogram, with INSTALL and UPDATE buckets?  Alternately, would it
make sense to break down the Result histogram by whether the update was
triggered manually vs. automatically?

[Sorin Jianu, 2016/03/09 19:51:43]

I combined the Install and Update in one histogram.

+  <owner>sorin@chromium.org</owner>
+  <summary>
+    The number of times the component updater called UpdateClient::Update. This
+    corresponds to the number of automated component update checks.
+  </summary>
+</histogram>
+
+<histogram name="ComponentUpdater.Update.Result" enum="BooleanError">
+  <owner>sorin@chromium.org</owner>
+  <summary>The result of an install or an update check.</summary>
+</histogram>
+
+<histogram name="ComponentUpdater.UpdateCompleteTime" units="Ms">

[Ilya Sherman, 2016/03/09 02:28:00]

nit: s/Ms/ms

[Sorin Jianu, 2016/03/09 19:51:43]

Done.

+  <owner>sorin@chromium.org</owner>
+  <summary>
+    Time to complete an Install or an Update component update call.
+  </summary>
+</histogram>
+
 <histogram
     name="Compositing.Browser.DisplayListRecordingSource.UpdateInvalidatedAreaPerMs"
     units="pixels/ms">