Refactor ClipboardRecentContent singleton creation.

components/open_from_clipboard/clipboard_recent_content.cc

+// Copyright 2015 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 "components/open_from_clipboard/clipboard_recent_content.h"
+
+#include "base/logging.h"
+
+namespace {
+ClipboardRecentContent* g_clipboard_recent_content = nullptr;
+}
+
+ClipboardRecentContent::ClipboardRecentContent() {}
+
+ClipboardRecentContent::~ClipboardRecentContent() {}
+
+// static
+ClipboardRecentContent* ClipboardRecentContent::GetInstance() {
+  DCHECK(g_clipboard_recent_content);
+  return g_clipboard_recent_content;
+}
+
+// static
+void ClipboardRecentContent::SetInstance(ClipboardRecentContent* instance) {
+  g_clipboard_recent_content = instance;
+}