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..581907034a8dbcf13252b42dafd6f16e0790d1ff 100644
--- a/chrome/browser/chrome_browser_main.cc
+++ b/chrome/browser/chrome_browser_main.cc
@@ -637,6 +637,11 @@ void ChromeBrowserMainParts::SetupMetricsAndFieldTrials() {
     base::FieldTrial::EnableBenchmarking();
   }
 
+  if (command_line->HasSwitch(switches::kForceFieldTrialParams)) {
+    variations::AssociateParamsFromString(
+      command_line->GetSwitchValueASCII(switches::kForceFieldTrialParams));
+  }
+
   // Ensure any field trials specified on the command line are initialized.
   if (command_line->HasSwitch(switches::kForceFieldTrials)) {
     std::set<std::string> unforceable_field_trials;