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

content/renderer/renderer_main.cc

Index: content/renderer/renderer_main.cc
diff --git a/content/renderer/renderer_main.cc b/content/renderer/renderer_main.cc
index 634684c58fe2fabf8f591cbaf00159ea557d58d0..31b0781833079d476e37190e38ae867850a430ab 100644
--- a/content/renderer/renderer_main.cc
+++ b/content/renderer/renderer_main.cc
@@ -193,7 +193,8 @@ int RendererMain(const MainFunctionParams& parameters) {
     // reported in crash reports.
     bool result = base::FieldTrialList::CreateTrialsFromString(
         parsed_command_line.GetSwitchValueASCII(switches::kForceFieldTrials),
-        base::FieldTrialList::ACTIVATE_TRIALS);
+        base::FieldTrialList::ACTIVATE_TRIALS,
+        std::set<std::string>());
     DCHECK(result);
   }