Adding a fourth omnibox prerender experiment.

chrome/browser/prerender/prerender_field_trial.h

 // Copyright (c) 2011 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.
 
 #ifndef CHROME_BROWSER_PRERENDER_PRERENDER_FIELD_TRIAL_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_FIELD_TRIAL_H_
 
 #include <string>
 
 class CommandLine;
 class Profile;
 
 namespace prerender {
 
 enum OmniboxHeuristic {
   OMNIBOX_HEURISTIC_ORIGINAL,
   OMNIBOX_HEURISTIC_CONSERVATIVE,
   OMNIBOX_HEURISTIC_EXACT,
+  OMNIBOX_HEURISTIC_EXACT_FULL,
   OMNIBOX_HEURISTIC_MAX
 };
 
 // Parse the --prerender= command line switch, which controls both prerendering
 // and prefetching.  If the switch is unset, or is set to "auto", then the user
 // is assigned to a field trial.
 void ConfigurePrefetchAndPrerender(const CommandLine& command_line);
 
 // Returns true if the user has opted in or has been opted in to the
 // prerendering from Omnibox experiment.
 bool IsOmniboxEnabled(Profile* profile);
 
 // Returns the heuristic to use when determining if prerendering should be
 // attempted from the Omnibox. Governed by a field trial.
 OmniboxHeuristic GetOmniboxHeuristicToUse();
 
 // Returns the suffix to use for histograms dependent on which Omnibox heuristic
 // is active.
 std::string GetOmniboxHistogramSuffix();
 
 }  // namespace prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_FIELD_TRIAL_H_