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

chrome/browser/ui/search/search.cc

Index: chrome/browser/ui/search/search.cc
diff --git a/chrome/browser/ui/search/search.cc b/chrome/browser/ui/search/search.cc
index 796edb4ee64bf23013c73c455ea65b7d8c84b63d..f2a40110ffe5e2432596026144f8a8c51cce3623 100644
--- a/chrome/browser/ui/search/search.cc
+++ b/chrome/browser/ui/search/search.cc
@@ -33,6 +33,10 @@ const bool kEnableOnThemesDefault = false;
 const char kEmbeddedPageVersionFlagName[] = "espv";
 const int kEmbeddedPageVersionDefault = 1;
 
+const char kInstantExtendedActivationName[] = "instant";
+const chrome::search::InstantExtendedDefault kInstantExtendedActivationDefault =
+    chrome::search::INSTANT_USE_EXISTING;
+
 // Constants for the field trial name and group prefix.
 const char kInstantExtendedFieldTrialName[] = "InstantExtended";
 const char kGroupNumberPrefix[] = "Group";
@@ -46,6 +50,33 @@ const char kDisablingSuffix[] = "DISABLED";
 namespace chrome {
 namespace search {
 
+InstantExtendedDefault InstantExtendedDefaultFromInt64(int64 default_value) {

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

I usually prefer having functions not available outside this source file (e.g.,
not declared in any header file), to be part of unnamed namespace.

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

Ordinarily I would have, but since most of this function uses stuff in the
chrome::search:: namespace it got really verbose. Ask me again and I'll move it
if you want :)

[MAD, 2013/01/31 20:14:53]

OK... Forget it...

+  switch (default_value) {
+    case 0: return INSTANT_FORCE_ON;
+    case 1: return INSTANT_USE_EXISTING;
+    case 2: return INSTANT_FORCE_OFF;
+    default: return INSTANT_USE_EXISTING;
+  }
+}
+
+InstantExtendedDefault GetInstantExtendedDefaultSetting() {
+  InstantExtendedDefault default_setting = INSTANT_USE_EXISTING;
+
+  FieldTrialFlags flags;
+  uint64 group_number = 0;
+  base::FieldTrial* trial =
+      base::FieldTrialList::Find(kInstantExtendedFieldTrialName);

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

There's also a method on FieldTrialList to get the group name directly. It
returns an empty string if the trial isn't active, so provide what you're
looking for here in a single call. I guess the ones who wrote/reviewed the code
you copied from below didn't know about it... :-)

I wonder if there could be a way to extract this common code somehow...

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

Used the method you suggest. With the refactoring now done, this code isn't long
enough to be worth extracting imo.

[MAD, 2013/01/31 20:14:53]

Agreed...

+  if (trial && GetFieldTrialInfo(trial->group_name(), &flags, &group_number)) {
+    uint64 trial_default = GetUInt64ValueForFlagWithDefault(
+        kInstantExtendedActivationName,
+        kInstantExtendedActivationDefault,
+        flags);
+    default_setting = InstantExtendedDefaultFromInt64(trial_default);
+  }
+
+  return default_setting;
+}
+
 // Check whether or not the Extended API should be used on the given profile.
 bool IsInstantExtendedAPIEnabled(Profile* profile) {
   return EmbeddedSearchPageVersion(profile) != 0;
@@ -66,12 +97,7 @@ uint64 EmbeddedSearchPageVersion(Profile* profile) {
   uint64 group_number = 0;
   base::FieldTrial* trial =
       base::FieldTrialList::Find(kInstantExtendedFieldTrialName);
-  if (trial) {
-    std::string group_name = trial->group_name();
-    GetFieldTrialInfo(group_name, &flags, &group_number);
-  }
-
-  if (group_number > 0) {
+  if (trial && GetFieldTrialInfo(trial->group_name(), &flags, &group_number)) {
     uint64 espv = GetUInt64ValueForFlagWithDefault(
         kEmbeddedPageVersionFlagName,
         kEmbeddedPageVersionDefault,
@@ -153,9 +179,10 @@ bool IsForcedInstantURL(const GURL& url) {
 
 // Given a field trial group name in the above format, parses out the group
 // number and configuration flags.  Will return a group number of 0 on error.
-void GetFieldTrialInfo(const std::string& group_name,
+bool GetFieldTrialInfo(const std::string& group_name,

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

Now that we return success, group_number pointer could be optional (e.g., accept
NULL) since none of the calls in this file actually use it.

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

Done.

                        FieldTrialFlags* flags,
                        uint64* group_number) {
+  bool success = false;
   if (!EndsWith(group_name, kDisablingSuffix, true) &&
       StartsWithASCII(group_name, kGroupNumberPrefix, true)) {
     // We have a valid trial that starts with "Group" and isn't disabled.
@@ -168,12 +195,15 @@ void GetFieldTrialInfo(const std::string& group_name,
       base::SplitStringIntoKeyValuePairs(
           group_name.substr(first_space), ':', ' ', flags);
     }
-    if (!base::StringToUint64(group_prefix.substr(strlen(kGroupNumberPrefix)),
-                              group_number)) {
-      // Could not parse group number.
+    if (base::StringToUint64(group_prefix.substr(strlen(kGroupNumberPrefix)),
+                             group_number)) {
+      success = true;
+    } else {
       *group_number = 0;
     }
   }
+
+  return success;
 }
 
 // Given a FieldTrialFlags object, returns the string value of the provided