Convert ChromeViewMsg_SetFieldTrialGroup to use mojo.

chrome/common/field_trial_recorder.mojom

Index: chrome/common/field_trial_recorder.mojom
diff --git a/chrome/common/field_trial_recorder.mojom b/chrome/common/field_trial_recorder.mojom
deleted file mode 100644
index 007439d7a17735d999af9f9a0bf2ffc98b441263..0000000000000000000000000000000000000000
--- a/chrome/common/field_trial_recorder.mojom
+++ /dev/null
@@ -1,11 +0,0 @@
-// Copyright 2016 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-module chrome.mojom;
-
-// Records field trial activations from the renderers.
-interface FieldTrialRecorder {
-  // Indicates that a field trial has been activated.
-  FieldTrialActivated(string trial_name);
-};