Handle the Web Page Replay related Chrome flags in one place.

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 50d16f5dc8e0f4dc5607f6a3f39723295d4913d1..c95555f0dbb500beeb797b805508364bbd35ac40 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
+++ b/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
@@ -19,7 +19,6 @@ from telemetry.core import user_agent
 from telemetry.core import util
 from telemetry.core import web_contents
 from telemetry.core import wpr_modes
-from telemetry.core import wpr_server
 from telemetry.core.backends import browser_backend
 from telemetry.core.backends.chrome import extension_backend
 from telemetry.core.backends.chrome import system_info_backend
@@ -102,12 +101,7 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
 
     if self.browser_options.disable_background_networking:
       args.append('--disable-background-networking')
-
-    if self.browser_options.netsim:
-      args.append('--ignore-certificate-errors')
-    elif self.browser_options.wpr_mode != wpr_modes.WPR_OFF:
-      args.extend(wpr_server.GetChromeFlags(self.forwarder_factory.host_ip,
-                                            self.wpr_port_pairs))
+    args.extend(self.GetReplayBrowserStartupArgs())
     args.extend(user_agent.GetChromeUserAgentArgumentFromType(
         self.browser_options.browser_user_agent_type))
 
@@ -133,6 +127,34 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
 
     return args
 
+  def GetReplayBrowserStartupArgs(self):
+    if self.browser_options.wpr_mode == wpr_modes.WPR_OFF:
+      return []
+    # Use Chrome's --host-resolver-rules flag if the forwarder does not send
+    # 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 = ['--ignore-certificate-errors']
+    if use_host_resolver:
+      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
+    # are not the standard defaults.
+    # Backstory:
+    #     That allows Telemetry to pick ports that do not require sudo
+    #     and leaves room for multiple instances running simultaneously.
+    #     The default ports are required for network simulation.
+    if http_remote_port != 80:
+      replay_args.append('--testing-fixed-http-port=%s' % http_remote_port)
+    if https_remote_port != 443:  # check if using the default HTTPS port
+      replay_args.append('--testing-fixed-https-port=%s' % https_remote_port)
+    return replay_args
+
   def HasBrowserFinishedLaunching(self):
     try:
       self.Request('', timeout=.1)