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

content/public/common/content_switches.cc

Index: content/public/common/content_switches.cc
diff --git a/content/public/common/content_switches.cc b/content/public/common/content_switches.cc
index f9b5801177ce6e5ce67172934ce1a224e3b09237..da412c0e505ba399be2c19a628b623d8c5e697e5 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -529,6 +529,16 @@ const char kExtraPluginDir[]                = "extra-plugin-dir";
 // FieldTrialList::CreateTrialsFromString() in field_trial.h for details.
 const char kForceFieldTrials[]              = "force-fieldtrials";
 
+// This option can be used to force parameters of field trials when testing
+// changes locally. The argument is a list of key/value pairs prefixed by
+// Trial/Group pair. The following shows setting parameters to 2 experiments
+// where in the first, it forces "id" to be "foo" for the "Enabled" group of
+// the "EnhancedBookmarks" trial:
+// "EnhancedBookmarks.Enabled:id/foo,Experiment2.Group1:key1/value1"
+// See variations::AssociateParamsFromString() in variations_associated_data.h
+// for details.
+const char kForceFieldTrialParams[]        = "force-fieldtrial-params";
+
 // Always use the Skia GPU backend for drawing layer tiles. Only valid with GPU
 // accelerated compositing + impl-side painting. Overrides the
 // kEnableGpuRasterization flag.