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..ee64491e00db731c7c8b4afc49f0dc6408272b08 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -5138,6 +5138,28 @@ 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.Calls.Count" enum="ComponentUpdaterCalls">

[Ilya Sherman, 2016/03/09 20:13:50]

nit: I'd drop the "Count" suffix at this point -- every histogram is counting
something =)

[Sorin Jianu, 2016/03/09 22:26:21]

Done.

+  <owner>sorin@chromium.org</owner>
+  <summary>
+    The number of times the component updater called UpdateClient::Install or
+    UpdateClient::Update. These correspond to the number of manual component
+    update checks performed as a result of a user action, and the number of
+    automated component update checks.
+  </summary>
+</histogram>
+
+<histogram name="ComponentUpdater.UpdateCompleteResult" 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">
+  <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">
@@ -61151,6 +61173,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="2" label="Successful first layout"/>
 </enum>
 
+<enum name="ComponentUpdaterCalls" type="int">
+  <int value="0" label="Install"/>
+  <int value="1" label="Update"/>
+</enum>
+
 <enum name="CompositedScrolling" type="int">
   <int value="0" label="Is scrollable area"/>
   <int value="1" label="Needs to be stacking container"/>