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 1519047831fff0b41e65960d9ec3c19b55aa7d12..bf87b8421334e6b2cae459b42a854dd7f9bb6405 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -616,6 +616,19 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="AppBanners.BeforeInstallEvent"
+    enum="AppBannersBeforeInstallEvent">
+  <owner>dominickn@chromium.org</owner>
+  <summary>
+    App banners promote an application related to the current website, and are
+    requested specifically through the current page's HTML.  This stat tracks
+    usage of the BeforeInstallPromptEvent, which allows developers to control
+    when an app banner appears. The events in this histogram are not mutually
+    exclusive - for example, preventDefault() must be called if prompt() is
+    called.
+  </summary>
+</histogram>
+
 <histogram name="AppBanners.DismissEvent" enum="AppBannersDismissEvent">
   <owner>dfalcantara@chromium.org</owner>
   <summary>
@@ -65534,6 +65547,23 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="15" label="RESULT_WSC_NOT_AVAILABLE"/>
 </enum>
 
+<enum name="AppBannersBeforeInstallEvent" type="int">
+  <int value="1" label="BeforeInstallPromptEvent created and dispatched"/>
+  <int value="2"
+      label="BeforeInstallPromptEvent flow complete; continuing to show the
+             banner"/>
+  <int value="3" label="BeforeInstallPromptEvent not used to stop the banner"/>
+  <int value="4"
+      label="BeforeInstallPromptEvent.preventDefault() called to stop the
+             banner"/>
+  <int value="5"
+      label="BeforeInstallPromptEvent.prompt() called to show the banner
+             after preventDefault()"/>
+  <int value="6"
+      label="BeforeInstallPromptEvent.prompt() not called to show the banner
+             after preventDefault()"/>

[Ilya Sherman, 2016/07/06 23:15:53]

Optional nit: These labels are pretty long, which will likely make them hard to
read in the dashboard UI.  I'd recommend shortening them by omitting the shared
"BeforeInstallPromptEvent" prefix, and also omitting some of the explanatory
text, e.g. just "prompt() not called" (or maybe a bit of additional text to
clarify that this is only recorded when preventDefault() is called, if that's
true).  You can still include the explanatory text as on-hover text if you'd
like:

<int value="6" label="prompt() not
called">BeforeInstallPromptEvent.preventDefault() was called, and
BeforeInstallPromptEvent.prompt() was not subsequently called, so no banner was
shown.</int>

[dominickn, 2016/07/07 00:16:02]

Done.

+</enum>
+
 <enum name="AppBannersDismissEvent" type="int">
   <int value="41" label="Error/unknown reason for dismissal"/>
   <int value="42" label="User opened the application after installing it"/>