Add metrics to track Google Play install WebAPK failures.

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 baeafb30b2ed6acc17dc513735c857883a2932b8..4c2b1b6eed69dad77f5765d55bbaaf15df986e71 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -75975,6 +75975,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="WebApk.Install.GooglePlayInstallResult"
+    enum="WebApkGooglePlayInstallResult">
+  <owner>hanxi@chromium.org</owner>
+  <owner>pkotwicz@chromium.org</owner>
+  <owner>yfriedman@chromium.org</owner>
+  <summary>
+    Records whether installing WebAPKs from Google Play succeeded. If not,

[pkotwicz, 2017/03/21 16:59:39]

"WebAPKs" -> "WebAPK"

[Xi Han, 2017/03/21 18:43:45]

"a WebAPK"?

+    records the reason of failures sent by Google Play.

[pkotwicz, 2017/03/21 16:59:39]

"reason of failure" -> "failure reason"

[Xi Han, 2017/03/21 18:43:45]

Done.

+  </summary>
+</histogram>
+
 <histogram name="WebApk.Install.GooglePlayInstallState"
     enum="WebApkGooglePlayInstallState">
   <owner>hanxi@chromium.org</owner>
@@ -113272,6 +113283,20 @@ from previous Chrome versions.
   <int value="4" label="Session, Warmup"/>
 </enum>
 
+<enum name="WebApkGooglePlayInstallResult" type="int">
+  <int value="0" label="Success"/>
+  <int value="1" label="Install delegate unavailable"/>
+  <int value="2" label="Failed to connect to Google Play Install Service"/>
+  <int value="3" label="Caller verification failure"/>
+  <int value="4" label="Policy violation"/>
+  <int value="5" label="Play install API disabled"/>
+  <int value="6" label="Request to Play install API failed"/>
+  <int value="7" label="Download cancelled"/>
+  <int value="8" label="Download error"/>
+  <int value="9" label="Install error"/>
+  <int value="10" label="Install times out"/>

[pkotwicz, 2017/03/21 16:59:39]

Nit: "times out" -> "timed out"

[Xi Han, 2017/03/21 18:43:45]

Done.

+</enum>
+
 <enum name="WebApkGooglePlayInstallState" type="int">
   <int value="0" label="Play installation supported."/>
   <int value="1" label="Play installation disabled for other reason."/>