Convert ChromeViewHostMsg_UpdatedCacheStats to use mojo.

chrome/browser/cache_stats_recorder.cc

+// 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.
+
+#include "chrome/browser/cache_stats_recorder.h"
+
+#include "base/memory/ptr_util.h"
+#include "components/web_cache/browser/web_cache_manager.h"
+#include "mojo/public/cpp/bindings/strong_associated_binding.h"
+
+CacheStatsRecorder::CacheStatsRecorder(int render_process_id)
+    : render_process_id_(render_process_id) {}
+
+CacheStatsRecorder::~CacheStatsRecorder() = default;
+
+// static
+void CacheStatsRecorder::Create(
+    int render_process_id,
+    chrome::mojom::CacheStatsRecorderAssociatedRequest request) {
+  mojo::MakeStrongAssociatedBinding(
+      base::MakeUnique<CacheStatsRecorder>(render_process_id),
+      std::move(request));
+}
+
+void CacheStatsRecorder::RecordCacheStats(uint64_t capacity, uint64_t size) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  // XXX(nigeltao): do we have to do this on the UI thread??
+  web_cache::WebCacheManager::GetInstance()->ObserveStats(render_process_id_,

[Ken Rockot(use gerrit already), 2017/03/13 17:19:58]

IIUC this is clearly already happening on the IO thread today, so I'd say no.

+                                                          capacity, size);
+}