Make --force-fieldtrials not activate them in the browser process.

base/metrics/field_trial.cc

Index: base/metrics/field_trial.cc
===================================================================
--- base/metrics/field_trial.cc	(revision 208942)
+++ base/metrics/field_trial.cc	(working copy)
@@ -366,7 +366,8 @@
 }
 
 // static
-bool FieldTrialList::CreateTrialsFromString(const std::string& trials_string) {
+bool FieldTrialList::CreateTrialsFromString(const std::string& trials_string,
+                                            bool activate_trials) {
   DCHECK(global_);
   if (trials_string.empty() || !global_)
     return true;
@@ -391,7 +392,8 @@
     // Call |group()| to mark the trial as "used" and notify observers, if any.
     // This is needed to ensure the trial is properly reported in child process
     // crash reports.

[Ilya Sherman, 2013/06/28 00:58:07]

nit: Please move this comment inside the if-stmt, or else tweak it to be clear
that this only happens if |activate_trials| is set (and maybe why the behavior
sometimes isn't desirable).

[Alexei Svitkine (slow), 2013/06/28 17:05:15]

Done.

-    trial->group();
+    if (activate_trials)
+      trial->group();
   }
   return true;
 }