Add the Windows.IsPinnedToTaskbar metric.

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 c93a3e4fde61ad846cfec8685dcc8094dd64d4bc..ad64c1fd0d6ac63abcb64ba621ff82b5bb5c766b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -64446,6 +64446,31 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Windows.IsPinnedToTaskbar" enum="Boolean">
+  <owner>pmonette@chromium.org</owner>
+  <summary>
+    Indicates whether Chrome is pinned to the Windows taskbar for the current
+    user.

[Alexei Svitkine (slow), 2016/06/29 14:37:44]

Mention when this is logged. On start up?

[Patrick Monette, 2016/06/29 18:28:42]

Done.

+  </summary>
+</histogram>
+
+<histogram name="Windows.IsPinnedToTaskbar.ProcessError" enum="BooleanError">
+  <owner>pmonette@chromium.org</owner>
+  <summary>
+    Indicates whether a connection error occured between the browser and the
+    shell handler process. This is usually caused by a crash in the utility
+    process.
+  </summary>
+</histogram>
+
+<histogram name="Windows.IsPinnedToTaskbar.Succeeded" enum="BooleanSuccess">
+  <owner>pmonette@chromium.org</owner>
+  <summary>
+    Indicates whether an error occured while checking if Chrome is pinned to the
+    Windows taskbar for the current user.
+  </summary>
+</histogram>
+
 <histogram name="Windows.Kernel32Version" enum="WindowsVersion">
   <owner>scottmg@chromium.org</owner>
   <summary>