Convert ChromeViewHostMsg_UpdatedCacheStats to use mojo.

chrome/common/cache_stats_recorder.mojom

Index: chrome/common/cache_stats_recorder.mojom
diff --git a/chrome/common/cache_stats_recorder.mojom b/chrome/common/cache_stats_recorder.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..6040210cc3e5e8809dd4a845e64f32f682c6f266
--- /dev/null
+++ b/chrome/common/cache_stats_recorder.mojom
@@ -0,0 +1,10 @@
+// Copyright 2017 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 cache statistics sent from the renderer.
+interface CacheStatsRecorder {
+  RecordCacheStats(uint64 capacity, uint64 size);
+};