Histogram for FallbackDNSTestResult.

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 8aa92d57a4efedb0ce7f8c9e694bf0427e10b18a..379d10d72f890442222b896dd274c812ba950085 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -15969,6 +15969,16 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Network.Shill.Wifi.FallbackDNSTestResult"
+    enum="FallbackDNSTestResult">
+  <owner>zqiu@chromium.org</owner>
+  <summary>
+    Chrome OS network performance metric that tracks the result of the fallback
+    DNS test. The fallback DNS test is performed when portal detection failed
+    due to DNS failure.
+  </summary>
+</histogram>
+
 <histogram name="Network.Shill.WiFi.FrequenciesConnectedEver">
   <owner>quiche@chromium.org</owner>
   <summary>
@@ -35014,6 +35024,11 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="3" label="Unfused; lot ID NZVR7"/>
 </enum>
 
+<enum name="FallbackDNSTestResult" type="int">
+  <int value="0" label="Success"/>
+  <int value="1" label="Failure"/>
+</enum>
+
 <enum name="FallbackSSLVersion" type="int">
   <int value="0" label="FALLBACK_NONE">SSL version fallback did not occur.</int>
   <int value="1" label="FALLBACK_SSL3">Fell back on SSL 3.0.</int>