Allow controlling the Instant field trial through a command line flag.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index aa617a0e8ffed85a40bf7407c9b9c0d9d6f47501..14f539467584cb762c1c2aa9bdc585b6c743020b 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -669,6 +669,12 @@ const char kImportFromFile[]                = "import-from-file";
 // Causes the browser to launch directly in incognito mode.
 const char kIncognito[]                     = "incognito";
 
+// Control the Instant field trial. Valid values are defined below. If an
+// unknown value is supplied on the command line, the field trial is disabled.
+const char kInstantFieldTrial[]             = "instant-field-trial";
+// The field trial is forced into the INSTANT_EXPERIMENT group.
+const char kInstantFieldTrialInstant[]      = "instant";
+
 // URL to use for instant. If specified this overrides the url from the
 // TemplateURL.
 const char kInstantURL[]                    = "instant-url";