Linux native notifications: Support closing and updating notifications

ui/base/glib/scoped_gobject.h

+// 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.
+
+#ifndef UI_BASE_GLIB_SCOPED_GOBJECT_H_
+#define UI_BASE_GLIB_SCOPED_GOBJECT_H_
+
+#include "base/logging.h"
+
+// Similar in spirit to a std::unique_ptr.
+template <typename T>
+class ScopedGObject {
+ public:
+  ScopedGObject() : obj_(nullptr) {}
+
+  explicit ScopedGObject(T* obj) : obj_(obj) {
+    // Remove the floating reference from |obj_| if it has one.

[sky, 2017/04/06 20:44:46]

Should reset() get this logic too? If not, why?

[Tom (Use chromium acct), 2017/04/06 22:28:57]

Yes it should!  Thanks for catching this!

+    if (g_object_is_floating(obj_))
+      g_object_ref_sink(obj_);
+    DCHECK(G_OBJECT(obj_)->ref_count == 1);
+  }
+
+  ScopedGObject(const ScopedGObject<T>& other) = delete;
+
+  ScopedGObject(ScopedGObject<T>&& other) : obj_(other.obj_) {
+    other.obj_ = nullptr;
+  }
+
+  ~ScopedGObject() { reset(); }
+
+  ScopedGObject<T>& operator=(const ScopedGObject<T>& other) = delete;
+
+  ScopedGObject<T>& operator=(ScopedGObject<T>&& other) {
+    g_object_unref(obj_);

[sky, 2017/04/06 20:44:46]

reset() ?

[Tom (Use chromium acct), 2017/04/06 22:28:57]

Done.

+    obj_ = other.obj_;
+    other.obj_ = nullptr;
+    return *this;
+  }
+
+  operator T*() { return obj_; }
+
+  void reset(T* obj = nullptr) {
+    if (obj_)
+      Unref();

[sky, 2017/04/06 20:44:46]

It's mildly confusing that you have both reset and Unref. How about putting the
implementation of Unref() here and removing Unref?

[Tom (Use chromium acct), 2017/04/06 22:28:57]

Can't unfortunately.  We require a template override for GtkStyleContext
https://cs.chromium.org/chromium/src/chrome/browser/ui/libgtkui/gtk_util.h?rc...

[sky, 2017/04/06 23:30:17]

Subtle! Please add a comment about that as it's easy to miss.

+    obj_ = obj;
+  }
+
+ private:
+  void Unref() { g_object_unref(obj_); }
+
+  T* obj_;
+};
+
+#endif  // UI_BASE_GLIB_SCOPED_GOBJECT_H_