[Prerender] Get the prerender mode from Finch field trial.

chrome/browser/prerender/prerender_browsertest.cc

Index: chrome/browser/prerender/prerender_browsertest.cc
diff --git a/chrome/browser/prerender/prerender_browsertest.cc b/chrome/browser/prerender/prerender_browsertest.cc
index 2816636b2782612e5142796f36e63f05b3cebaa2..e3a825003568754f004810fe99c54dcdf02b9ad8 100644
--- a/chrome/browser/prerender/prerender_browsertest.cc
+++ b/chrome/browser/prerender/prerender_browsertest.cc
@@ -574,12 +574,6 @@ class PrerenderBrowserTest : public test_utils::PrerenderInProcessBrowserTest {
                                 expected_number_of_loads);
   }
 
-  void SetUpCommandLine(base::CommandLine* command_line) override {
-    PrerenderInProcessBrowserTest::SetUpCommandLine(command_line);
-    command_line->AppendSwitchASCII(switches::kPrerenderMode,
-                                    switches::kPrerenderModeSwitchValueEnabled);
-  }
-
   void SetUpInProcessBrowserTestFixture() override {
     test_utils::PrerenderInProcessBrowserTest::
         SetUpInProcessBrowserTestFixture();
@@ -2625,7 +2619,6 @@ class PrerenderBrowserTestWithExtensions : public PrerenderBrowserTest,
   void SetUp() override { PrerenderBrowserTest::SetUp(); }
 
   void SetUpCommandLine(base::CommandLine* command_line) override {
-    PrerenderBrowserTest::SetUpCommandLine(command_line);
     ExtensionApiTest::SetUpCommandLine(command_line);
   }
 
@@ -3297,7 +3290,6 @@ class PrerenderBrowserTestWithNaCl : public PrerenderBrowserTest {
   ~PrerenderBrowserTestWithNaCl() override {}
 
   void SetUpCommandLine(base::CommandLine* command_line) override {
-    PrerenderBrowserTest::SetUpCommandLine(command_line);
     command_line->AppendSwitch(switches::kEnableNaCl);
   }
 };