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

chrome/browser/chrome_browser_field_trials.h

Index: chrome/browser/chrome_browser_field_trials.h
diff --git a/chrome/browser/chrome_browser_field_trials.h b/chrome/browser/chrome_browser_field_trials.h
index 48467d54212e91e6d491d6c602bbf4fd12e6bd63..4b22f76cbaafc713af6888219d1ee038cbd6a715 100644
--- a/chrome/browser/chrome_browser_field_trials.h
+++ b/chrome/browser/chrome_browser_field_trials.h
@@ -5,7 +5,6 @@
 #ifndef CHROME_BROWSER_CHROME_BROWSER_FIELD_TRIALS_H_
 #define CHROME_BROWSER_CHROME_BROWSER_FIELD_TRIALS_H_
 
-#include "base/command_line.h"
 #include "base/macros.h"
 
 namespace base {
@@ -14,7 +13,7 @@ class FeatureList;
 
 class ChromeBrowserFieldTrials {
  public:
-  explicit ChromeBrowserFieldTrials(const base::CommandLine& command_line);
+  ChromeBrowserFieldTrials();
   ~ChromeBrowserFieldTrials();
 
   void SetupFieldTrials();
@@ -33,8 +32,6 @@ class ChromeBrowserFieldTrials {
   // reported as used.
   void InstantiateDynamicTrials();
 
-  const base::CommandLine& parsed_command_line_;
-
   DISALLOW_COPY_AND_ASSIGN(ChromeBrowserFieldTrials);
 };