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

chrome/browser/prerender/prerender_unittest.cc

Index: chrome/browser/prerender/prerender_unittest.cc
diff --git a/chrome/browser/prerender/prerender_unittest.cc b/chrome/browser/prerender/prerender_unittest.cc
index 68d6c5bbddbb4f1c7dbcc19977ddbac1ab8352a3..445639d6f98388f41a141e34978f8e2bb6f15027 100644
--- a/chrome/browser/prerender/prerender_unittest.cc
+++ b/chrome/browser/prerender/prerender_unittest.cc
@@ -15,6 +15,7 @@
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/field_trial.h"
 #include "base/strings/stringprintf.h"
+#include "base/test/scoped_feature_list.h"
 #include "base/test/simple_test_clock.h"
 #include "base/test/simple_test_tick_clock.h"
 #include "base/time/time.h"
@@ -411,12 +412,12 @@ class PrerenderTest : public testing::Test {
 TEST_F(PrerenderTest, PrerenderRespectsDisableFlag) {
   RestorePrerenderMode restore_prerender_mode;
   ASSERT_TRUE(PrerenderManager::IsPrerenderingPossible());
-  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
-  command_line->AppendSwitchASCII(
-    switches::kPrerenderMode,
-    switches::kPrerenderModeSwitchValueDisabled);
-  prerender::ConfigurePrerender(*command_line);
-  ASSERT_FALSE(PrerenderManager::IsPrerenderingPossible());
+  {
+    base::test::ScopedFeatureList scoped_feature_list;
+    scoped_feature_list.InitAndDisableFeature(kNoStatePrefetchFeature);
+    prerender::ConfigurePrerender();
+    ASSERT_FALSE(PrerenderManager::IsPrerenderingPossible());
+  }
 }
 
 TEST_F(PrerenderTest, PrerenderRespectsThirdPartyCookiesPref) {