Always use --host-resolver-rules Chrome flag with ChromeOS

tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py

Index: tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
diff --git a/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py b/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
index 33d6b7005169bd57a79085768b8719a2296453d8..f2131f9afa3dd3d5f59a9eb3af536d91d3d7529d 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
+++ b/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
@@ -127,6 +127,20 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
 
     return args
 
+  @property
+  def _use_host_resolver_rules(self):
+    """Returns True if need --host-resolver-rules to send requests to replay."""
+    if self.browser_options.netsim:
+      # Avoid --host-resolver-rules with netsim because it causes Chrome to
+      # skip DNS requests. With netsim, we want to exercise DNS requests.
+      return False
+    if self.forwarder_factory.does_forwarder_override_dns:
+      # Avoid --host-resolver-rules when the forwarder can map DNS requests
+      # from devices to the replay DNS port on the host running Telemetry.
+      # This allows the browser to exercise DNS requests.
+      return False
+    return True
+
   def GetReplayBrowserStartupArgs(self):
     if self.browser_options.wpr_mode == wpr_modes.WPR_OFF:
       return []
@@ -134,9 +148,6 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
     # the HTTP requests directly to Replay. Also use --host-resolver-rules
     # without netsim. With netsim, DNS requests should be sent (to get the
     # simulated latency), however, the flag causes DNS requests to be skipped.
-    use_host_resolver = (
-        not self.forwarder_factory.does_forwarder_override_dns and
-        not self.browser_options.netsim)
     http_remote_port = self.wpr_port_pairs.http.remote_port
     https_remote_port = self.wpr_port_pairs.https.remote_port
     replay_args = []
@@ -145,7 +156,7 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
       # and installed a root certificate. When |self.wpr_ca_cert_path| is
       # set, Web Page Replay uses it to sign HTTPS responses.
       replay_args.append('--ignore-certificate-errors')
-    if use_host_resolver:
+    if self._use_host_resolver_rules:
       replay_args.append('--host-resolver-rules=MAP * %s,EXCLUDE localhost' %
                          self.forwarder_factory.host_ip)  # replay's host_ip
     # Force the browser to send HTTP/HTTPS requests to fixed ports if they