Add a mechanism to force parameters of a group to a specific value.

chrome/browser/chrome_browser_main.cc

Index: chrome/browser/chrome_browser_main.cc
diff --git a/chrome/browser/chrome_browser_main.cc b/chrome/browser/chrome_browser_main.cc
index a76aad93798539087c964a55c5692541c458613e..111d9e7bc15b80c308937d17c57b148bbce93942 100644
--- a/chrome/browser/chrome_browser_main.cc
+++ b/chrome/browser/chrome_browser_main.cc
@@ -103,6 +103,7 @@
 #include "chrome/common/net/net_resource_provider.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/profiling.h"
+#include "chrome/common/variations/variations_util.h"
 #include "chrome/grit/generated_resources.h"
 #include "chrome/installer/util/google_update_settings.h"
 #include "components/component_updater/component_updater_service.h"
@@ -637,6 +638,13 @@ void ChromeBrowserMainParts::SetupMetricsAndFieldTrials() {
     base::FieldTrial::EnableBenchmarking();
   }
 
+  if (command_line->HasSwitch(switches::kForceFieldTrialParams)) {
+    bool result = chrome_variations::AssociateParamsFromString(
+        command_line->GetSwitchValueASCII(switches::kForceFieldTrialParams));
+    CHECK(result) << "Invalid --" << switches::kForceFieldTrialParams
+                  << " list specified.";
+  }
+
   // Ensure any field trials specified on the command line are initialized.
   if (command_line->HasSwitch(switches::kForceFieldTrials)) {
     std::set<std::string> unforceable_field_trials;