[Telemetry] Enable background networking for tab_switching measurements

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 e22a0db6fe671ed4c928c9b1aa44f2a1b7f1338b..4306c9707ba7800a725e199c71ac8a9fe8c1d45a 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
+++ b/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
@@ -83,7 +83,6 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
   def GetBrowserStartupArgs(self):
     args = []
     args.extend(self.browser_options.extra_browser_args)
-    args.append('--disable-background-networking')
     args.append('--enable-net-benchmarking')
     args.append('--metrics-recording-only')
     args.append('--no-default-browser-check')
@@ -101,6 +100,9 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
     if not '--enable-spdy-proxy-auth' in args:
       args.append('--no-proxy-server')
 
+    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: