Add WebAPK installation metrics.

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 ccb015218961048b5dfb1b1cfa73160813bd231d..c26db4d044cb882c72bef0a7a41aec573ecb3cff 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -65209,6 +65209,43 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="WebApk.Install.InstallEvent" enum="WebApkInstallEvent">
+  <owner>hanxi@chromium.org</owner>
+  <owner>pkotwicz@chromium.org</owner>
+  <owner>yfriedman@chromium.org</owner>
+  <summary>
+    WebAPKs are installed via App banners or via user clicking Add-To-Homescreen
+    from the app menu. This stat tracks the WebAPKs installation events,
+    including whether the banner is ignored, whether the banner is dismissed by
+    user before or during the installation, as well as whether the installation
+    is sucessful or failed.
+  </summary>
+</histogram>
+
+<histogram name="WebApk.Install.StartType" enum="WebApkStartType">
+  <owner>hanxi@chromium.org</owner>
+  <owner>pkotwicz@chromium.org</owner>
+  <owner>yfriedman@chromium.org</owner>
+  <summary>
+    WebApks are installed via App banners or via user clicking Add-To-Homescreen
+    from the app menu. If the installation is via app banner, user could either
+    accept to install or dismiss the banner; while via Add-To-Homescreen menu,
+    the installation will start automatically. This stat tracks whether the
+    installation is triggered by app banner, as well as the ways that user
+    accepets to install a WebAPK.
+  </summary>
+</histogram>
+
+<histogram name="WebApk.Install.UserAction" enum="WebApkUserAction">
+  <owner>hanxi@chromium.org</owner>
+  <owner>pkotwicz@chromium.org</owner>
+  <owner>yfriedman@chromium.org</owner>
+  <summary>
+    This stat tracks whether user clicks the Open button on the banner after a
+    WebAPK is installed.
+  </summary>
+</histogram>
+
 <histogram name="Webapp.Splashscreen.BackgroundColor"
     enum="SplashscreenColorStatus">
   <owner>mlamouri@chromium.org</owner>
@@ -97817,6 +97854,25 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="4" label="Session, Warmup"/>
 </enum>
 
+<enum name="WebApkInstallEvent" type="int">
+  <int value="0" label="Banner is ignored"/>
+  <int value="1" label="Banner with the Add-to-Homescreen button is dismissed"/>
+  <int value="2" label="Banner with the Adding button is dismissed"/>
+  <int value="3" label="Success"/>
+  <int value="4" label="Failed"/>
+</enum>
+
+<enum name="WebApkStartType" type="int">
+  <int value="0" label="Installation triggered from the banner"/>
+  <int value="1" label="Installation started from the banner"/>
+  <int value="2" label="Installation started from the Add-to-Homescreen menu"/>
+</enum>
+
+<enum name="WebApkUserAction" type="int">
+  <int value="0" label="Open button clicked"/>
+  <int value="1" label="Open button dismissed"/>
+</enum>
+
 <enum name="WebBluetoothConnectGATTOutcome" type="int">
   <int value="0" label="Success"/>
   <int value="1" label="Device no longer in range"/>