Fixed IsFirewallReady histogram name.

https://codereview.chromium.org/260283002/ had different names.

NOTRY=true

Review URL: https://codereview.chromium.org/261753010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@267938 0039d316-1c4b-4281-b951-d872f2087c98

tools/metrics/histograms/histograms.xml

@@ -8602,7 +8602,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
-<histogram name="LocalDiscovery.FirewallState" enum="BooleanEnabled">
+<histogram name="LocalDiscovery.IsFirewallReady" enum="BooleanEnabled">
   <owner>noamsml@chromium.org</owner>
   <owner>vitalybuka@chromium.org</owner>
   <summary>