Convert ChromeViewMsg_SetFieldTrialGroup to use mojo.

chrome/common/renderer_configuration.mojom

Index: chrome/common/renderer_configuration.mojom
diff --git a/chrome/common/renderer_configuration.mojom b/chrome/common/renderer_configuration.mojom
index 851167c743aba7cd62f0bb32fc96680069d4674b..4dc1f6533155af35735399ebf94a14d59738023d 100644
--- a/chrome/common/renderer_configuration.mojom
+++ b/chrome/common/renderer_configuration.mojom
@@ -15,4 +15,10 @@ interface RendererConfiguration {
   // Set the content setting rules stored by the renderer.
   SetContentSettingRules(
       content_settings.mojom.RendererContentSettingRules rules);
+
+  // Tells the renderer to create a FieldTrial, and by using a 100% probability
+  // for the FieldTrial, forces the FieldTrial to have assigned group name.
+  //
+  // See base/metrics/field_trial.h for more information.
+  SetFieldTrialGroup(string trial_name, string group_name);
 };