Cronet: Use stale DNS cache entries experimentally.

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 aafa1dc4ba415150e605da6c1b93e96508463bdc..6470ca1c627bfcd5457087dbb3f61897141ba218 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -9203,6 +9203,25 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="DNS.StaleHostResolverRequestOutcome"
+    enum="DNS.StaleHostResolverRequestOutcome">
+  <owner>juliatuttle@chromium.org</owner>
+  <summary>
+    When a DNS request made through StaleHostResolver returns or is canceled,
+    the outcome of the request.
+  </summary>
+</histogram>
+
+<histogram name="DNS.StaleHostResolverStaleDelta"
+    enum="DNS.AddressListDeltaType">
+  <owner>juliatuttle@chromium.org</owner>
+  <summary>
+    When a DNS request made through StaleHostResolver receives results from the
+    network, also had stale cached results, and both results are successful, the
+    difference between the old and new address lists.
+  </summary>
+</histogram>
+
 <histogram name="DNS.TotalTime" units="ms">
   <owner>juliatuttle@chromium.org</owner>
   <summary>
@@ -65922,6 +65941,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="2" label="Updated stale entry"/>
 </enum>
 
+<enum name="DNS.StaleHostResolverRequestOutcome" type="int">
+  <int value="0"
+      label="Returned synchronously (cache, hosts, IP literal etc.)"/>
+  <int value="1" label="Returned network result; no stale result available."/>
+  <int value="2" label="Returned network result; stale result available."/>
+  <int value="3" label="Returned stale result; network was too slow."/>
+  <int value="4" label="Canceled; no stale result available."/>
+  <int value="5" label="Canceled; stale result available."/>
+</enum>
+
 <enum name="DNSEmptyAddressListAndNoError" type="int">
   <int value="0" label="Error reported or Address List is not empty"/>
   <int value="1" label="Success reported but Address List is empty"/>