Make some field trials unforceable via command-line in the official build.

base/metrics/field_trial.cc

Index: base/metrics/field_trial.cc
diff --git a/base/metrics/field_trial.cc b/base/metrics/field_trial.cc
index f718ab0371fa3b05cc6be4e0a0ab254e820c1e71..4aa1c151e8e5166439254513e21991c76c8d51c4 100644
--- a/base/metrics/field_trial.cc
+++ b/base/metrics/field_trial.cc
@@ -7,6 +7,7 @@
 #include <algorithm>
 
 #include "base/build_time.h"
+#include "base/callback.h"
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "base/sha1.h"
@@ -399,8 +400,10 @@ void FieldTrialList::GetActiveFieldTrialGroups(
 }
 
 // static
-bool FieldTrialList::CreateTrialsFromString(const std::string& trials_string,
-                                            FieldTrialActivationMode mode) {
+bool FieldTrialList::CreateTrialsFromString(
+    const std::string& trials_string,
+    FieldTrialActivationMode mode,
+    const IsAcceptedFieldTrialCallback& is_accepted_callback) {
   DCHECK(global_);
   if (trials_string.empty() || !global_)
     return true;
@@ -419,14 +422,16 @@ bool FieldTrialList::CreateTrialsFromString(const std::string& trials_string,
                            group_name_end - name_end - 1);
     next_item = group_name_end + 1;
 
-    FieldTrial* trial = CreateFieldTrial(name, group_name);
-    if (!trial)
-      return false;
-    if (mode == ACTIVATE_TRIALS) {
-      // Call |group()| to mark the trial as "used" and notify observers, if
-      // any. This is useful to ensure that field trials created in child
-      // processes are properly reported in crash reports.
-      trial->group();
+    if (is_accepted_callback.is_null() || is_accepted_callback.Run(name)) {
+      FieldTrial* trial = CreateFieldTrial(name, group_name);
+      if (!trial)
+        return false;
+      if (mode == ACTIVATE_TRIALS) {
+        // Call |group()| to mark the trial as "used" and notify observers, if
+        // any. This is useful to ensure that field trials created in child
+        // processes are properly reported in crash reports.
+        trial->group();
+      }
     }
   }
   return true;