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

chrome/common/chrome_switches.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Defines the shared command-line switches used by code in the Chrome
 // directory that don't have anywhere more specific to go.
 
 #ifndef CHROME_COMMON_CHROME_SWITCHES_H_
 #define CHROME_COMMON_CHROME_SWITCHES_H_
 
@@ skipping 197 matching lines @@
 extern const char kPackExtensionKey[];
 extern const char kParentProfile[];
 extern const char kPermissionRequestApiScope[];
 extern const char kPermissionRequestApiUrl[];
 extern const char kPpapiFlashPath[];
 extern const char kPpapiFlashVersion[];
 extern const char kPrerenderFromOmnibox[];
 extern const char kPrerenderFromOmniboxSwitchValueAuto[];
 extern const char kPrerenderFromOmniboxSwitchValueDisabled[];
 extern const char kPrerenderFromOmniboxSwitchValueEnabled[];
-extern const char kPrerenderMode[];
-extern const char kPrerenderModeSwitchValueDisabled[];
-extern const char kPrerenderModeSwitchValueEnabled[];
-extern const char kPrerenderModeSwitchValuePrefetch[];
-extern const char kPrerenderModeSwitchValueSimpleLoad[];
 extern const char kPrivetIPv6Only[];
 extern const char kProductVersion[];
 extern const char kProfileDirectory[];
 extern const char kProfilingAtStart[];
 extern const char kProfilingFlush[];
 extern const char kProxyAutoDetect[];
 extern const char kProxyBypassList[];
 extern const char kProxyPacUrl[];
 extern const char kProxyServer[];
 extern const char kPurgeAndSuspendTime[];
@@ skipping 170 matching lines @@
 #if defined(OS_WIN)
 bool GDITextPrintingEnabled();
 #endif
 
 // DON'T ADD RANDOM STUFF HERE. Put it in the main section above in
 // alphabetical order, or in one of the ifdefs (also in order in each section).
 
 }  // namespace switches
 
 #endif  // CHROME_COMMON_CHROME_SWITCHES_H_