Add metrics for Webstore Gallery Widget app

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 d78c1e18eac257744541042fcae2b1247c1d4d07..7e082e93cda5659d400d0137c6bc575d4006a02b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -49019,6 +49019,38 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="WebstoreWidgetApp.Close" enum="SuggestAppsDialogCloseReason">
+  <owner>joshwoodward@google.com</owner>
+  <summary>
+    Webstore Widget app: the reason why the suggest apps dialog was closed.
+  </summary>
+</histogram>
+
+<histogram name="WebstoreWidgetApp.Install" enum="SuggestAppsDialogInstall">
+  <owner>joshwoodward@google.com</owner>
+  <summary>
+    Webstore Widget app: whether the Webstore item user selected was
+    successfully installed or not.
+  </summary>
+</histogram>
+
+<histogram name="WebstoreWidgetApp.Load" enum="SuggestAppsDialogLoad">
+  <owner>joshwoodward@google.com</owner>
+  <summary>
+    Webstore Widget app: whether the initialization of the dialog succeeded or
+    not.
+  </summary>
+</histogram>
+
+<histogram name="WebstoreWidgetApp.LoadTime" units="milliseconds">
+  <owner>joshwoodward@google.com</owner>
+  <summary>
+    Webstore Widget app: time to load the widget contained in the app. Measured
+    between the moment window appears and the moment all the contants in the app

[Ilya Sherman, 2015/06/25 21:40:30]

nit: "contants" -> "contents"

[tbarzic, 2015/06/25 22:31:09]

Done.

+    including the Chrome Webstore widget are ready.
+  </summary>
+</histogram>
+
 <histogram name="Win8.PageLoad" enum="Win8PageLoadType">
   <owner>zturner@chromium.org</owner>
   <summary>