Remove a check for valid DNS names in SystemHostResolverCall.

HostResolver already has a check before lookups reach that point. Added
a DCHECK instead. Also remove a histogram that was broken in
https://chromium-review.googlesource.com/569298.

Bug: 496468
Change-Id: Ie2f78c48c2d251e8c563323464270516a6a00ff3
Reviewed-on: https://chromium-review.googlesource.com/578168
Commit-Queue: Matt Menke <mmenke@chromium.org>
Reviewed-by: Miriam Gershenson <mgersh@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488416}

net/dns/host_resolver_proc.cc

@@ -7,7 +7,6 @@
 #include "build/build_config.h"
 
 #include "base/logging.h"
-#include "base/metrics/histogram_macros.h"
 #include "base/sys_byteorder.h"
 #include "net/base/address_list.h"
 #include "net/base/net_errors.h"
@@ -126,16 +125,9 @@ int SystemHostResolverCall(const std::string& host,
                            HostResolverFlags host_resolver_flags,
                            AddressList* addrlist,
                            int* os_error) {
-  // Make sure |host| is properly formed. Save the validity check result so that
-  // we can count how often invalid names (see |net::IsValidHostLabelCharacter|)
-  // successfully resolve, if ever. TODO(crbug.com/695474): Remove this when we
-  // no longer need the UMA metrics.
-  bool valid_hostname = false;
-  {
-    std::string out_ignored;
-    if (!DNSDomainFromDot(host, &out_ignored))
-      return ERR_NAME_NOT_RESOLVED;
-  }
+  // |host| should be a valid domain name. HostResolverImpl::Resolve has checks
+  // to fail early if this is not the case.
+  DCHECK(IsValidDNSDomain(host));
 
   if (os_error)
     *os_error = 0;
@@ -258,8 +250,6 @@ int SystemHostResolverCall(const std::string& host,
 
   *addrlist = AddressList::CreateFromAddrinfo(ai);
   freeaddrinfo(ai);
-  UMA_HISTOGRAM_BOOLEAN("Net.SuccessfulResolutionWithValidDNSName",
-                        valid_hostname);
   return OK;
 }
 

tools/metrics/histograms/histograms.xml

@@ -42367,6 +42367,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 
 <histogram name="Net.SuccessfulResolutionWithValidDNSName" enum="Boolean">
   <owner>palmer@chromium.org</owner>
+  <obsolete>
+    Removed in 07/2017.
+  </obsolete>
   <summary>
     True if a DNS name contains only characters for which
     |net::IsValidLabelCharacter| returns true. Used to see if we can deprecate