Use an experiment value to set the instant_extended.enabled pref default.

chrome/browser/ui/search/search.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.
 
 #ifndef CHROME_BROWSER_UI_SEARCH_SEARCH_H_
 #define CHROME_BROWSER_UI_SEARCH_SEARCH_H_
 
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/basictypes.h"
 
 class GURL;
 class Profile;
 
 namespace chrome {
 namespace search {
 
+enum InstantExtendedDefault {
+  INSTANT_FORCE_ON,      // Force the setting on if no other setting exists.
+  INSTANT_USE_EXISTING,  // Use same the value of the old instant.enabled pref.
+  INSTANT_FORCE_OFF,     // Force the setting off if no other setting exists.
+};
+
+// Returns an enum value indicating which mode to set the new
+// instant_extended.enabled pref to by default.
+InstantExtendedDefault GetInstantExtendedDefaultSetting();
+
 // Returns whether the Instant extended API is enabled for the given |profile|.
 // |profile| may not be NULL.
 bool IsInstantExtendedAPIEnabled(Profile* profile);
 
 // Returns the value to pass to the &espv cgi parameter when loading the
 // embedded search page from the user's default search provider.  Will be
 // 0 if the Instant Extended API is not enabled.
 uint64 EmbeddedSearchPageVersion(Profile* profile);
 
 // Force the instant extended API to be enabled for tests.
 void EnableInstantExtendedAPIForTesting();
 
 // Returns whether query extraction is enabled.  If
 // |IsInstantExtendedAPIEnabled()| and the profile is not off the record, then
 // this method will also return true.
 bool IsQueryExtractionEnabled(Profile* profile);
 
 // Force query extraction to be enabled for tests.
 void EnableQueryExtractionForTesting();
 
 // Returns true if |url| has the same scheme, host, port and path as the
 // Instant URL set via --instant-url.
 bool IsForcedInstantURL(const GURL& url);
 
 // Type for a collection of experiment configuration parameters.
 typedef std::vector<std::pair<std::string, std::string> > FieldTrialFlags;
 
 // Given a field trial group name, parses out the group number and configuration
 // flags.
 // Exposed for testing only.

[MAD, 2013/01/31 15:44:57]

Document return value?

[robertshield, 2013/01/31 18:56:52]

Done.

-void GetFieldTrialInfo(const std::string& group_name,
+bool GetFieldTrialInfo(const std::string& group_name,
                        FieldTrialFlags* flags,
                        uint64* group_number);
 
 // Given a FieldTrialFlags object, returns the string value of the provided
 // flag.
 // Exposed for testing only.
 std::string GetStringValueForFlagWithDefault(
     const std::string& flag,
     const std::string& default_value,
     FieldTrialFlags& flags);
 
 // Given a FieldTrialFlags object, returns the uint64 value of the provided
 // flag.
 // Exposed for testing only.
 uint64 GetUInt64ValueForFlagWithDefault(
     const std::string& flag, uint64 default_value, FieldTrialFlags& flags);
 
 // Given a FieldTrialFlags object, returns the bool value of the provided flag.
 // Exposed for testing only.
 bool GetBoolValueForFlagWithDefault(
     const std::string& flag, bool default_value, FieldTrialFlags& flags);
 
 }  // namespace search
 }  // namespace chrome
 
 #endif  // CHROME_BROWSER_UI_SEARCH_SEARCH_H_