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

chrome/browser/ui/search/search.h

Index: chrome/browser/ui/search/search.h
diff --git a/chrome/browser/ui/search/search.h b/chrome/browser/ui/search/search.h
index d7364b74e38501a170cda9738853e06223504ff7..bd51062f52f3a0059083dd0d5f36055b9217e742 100644
--- a/chrome/browser/ui/search/search.h
+++ b/chrome/browser/ui/search/search.h
@@ -17,6 +17,16 @@ 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);
@@ -47,7 +57,7 @@ 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);