[Android WebAPKs] Add UMA metric for ShellAPK version

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 e70d96f68604095edb1dddee7eb53ea855694a83..75e87a9f26e4712532d32664883fcd22c6b0207e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -78976,6 +78976,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="WebApk.ShellApkVersion">

[Ilya Sherman, 2017/05/05 22:46:52]

nit: Please add the attribute base="true", as this histogram name is not a
complete name on its own.

+  <owner>hanxi@chromium.org</owner>
+  <owner>pkotwicz@chromium.org</owner>
+  <owner>yfriedman@chromium.org</owner>
+  <summary>
+    Records WebAPK &quot;Shell APK version&quot; when the WebAPK is launched.
+    The &quot;Shell APK version&quot; is documented in shell_apk_version.gni
+  </summary>
+</histogram>
+
 <histogram name="WebApk.Update.RequestQueued" enum="WebApkUpdateRequestQueued">
   <owner>hanxi@chromium.org</owner>
   <owner>pkotwicz@chromium.org</owner>
@@ -91992,6 +92002,12 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <affected-histogram name="VRSessionVideoTime"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="WebApkType">
+  <suffix name="BrowserApk" label="Installed by Chrome"/>
+  <suffix name="UnboundApk" label="Not installed by Chrome"/>
+  <affected-histogram name="WebApk.ShellApkVersion"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="WebFontFamily">
   <suffix name="roboto" label="Roboto font"/>
   <suffix name="opensans" label="Open Sans font"/>