content: convert zoom notifications to observer usage

content/public/browser/host_zoom_map.cc

Index: content/public/browser/host_zoom_map.cc
diff --git a/content/public/browser/host_zoom_map.cc b/content/public/browser/host_zoom_map.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c38c08bf107bc4f5d32d7cfddb0e8fae9346d316
--- /dev/null
+++ b/content/public/browser/host_zoom_map.cc
@@ -0,0 +1,35 @@
+// Copyright (c) 2013 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 "content/public/browser/host_zoom_map.h"
+
+#include "content/browser/host_zoom_map_impl.h"
+
+namespace content {
+
+HostZoomMap::Observer::Observer() : host_zoom_map_(NULL) {
+}
+
+HostZoomMap::Observer::Observer(HostZoomMap* map) : host_zoom_map_(NULL) {
+  Observe(map);
+}
+
+HostZoomMap::Observer::~Observer() {
+  if (host_zoom_map_)
+    host_zoom_map_->RemoveObserver(this);
+}
+
+void HostZoomMap::Observer::Observe(HostZoomMap* map) {
+  if (host_zoom_map_)
+    host_zoom_map_->RemoveObserver(this);
+  host_zoom_map_ = static_cast<HostZoomMapImpl*>(map);
+  host_zoom_map_->AddObserver(this);
+}
+
+void HostZoomMap::Observer::HostZoomMapImplDestroyed() {
+  host_zoom_map_->RemoveObserver(this);
+  host_zoom_map_ = NULL;
+}
+
+}  // namespace content