Add default testing command line flags in UITestBase instead of ProxyLauncher.

chrome/test/automation/proxy_launcher.cc

Index: chrome/test/automation/proxy_launcher.cc
diff --git a/chrome/test/automation/proxy_launcher.cc b/chrome/test/automation/proxy_launcher.cc
index 895a2d0afc1211321822665d1830e9888c2e07a9..3a34e84987a0dac10180098e424615b05d56993a 100644
--- a/chrome/test/automation/proxy_launcher.cc
+++ b/chrome/test/automation/proxy_launcher.cc
@@ -348,9 +348,6 @@ bool ProxyLauncher::WaitForBrowserProcessToQuit(
 
 void ProxyLauncher::PrepareTestCommandline(CommandLine* command_line,
                                            bool include_testing_id) {
-  // Propagate commandline settings from test_launcher_utils.
-  test_launcher_utils::PrepareBrowserCommandLineForTests(command_line);
-
   // Add any explicit command line flags passed to the process.
   CommandLine::StringType extra_chrome_flags =
       CommandLine::ForCurrentProcess()->GetSwitchValueNative(