Restructure SDCH layering to allow more separation (observer/1->[0,n]

net/base/sdch_observer.cc

+// Copyright 2014 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 "net/base/sdch_observer.h"
+
+#include "base/logging.h"
+
+namespace net {
+
+SdchObserver::SdchObserver() : reference_count_(0) {}
+
+// Null implementations to allow subclasses to received just notifications
+// that they are interested in.
+void SdchObserver::OnGetDictionary(SdchManager* manager,
+                                   const GURL& request_url,
+                                   const GURL& dictionary_url) { }
+void SdchObserver::OnClearDictionaries(SdchManager* manager) {}
+
+void SdchObserver::AddRef() { ++reference_count_; }
+
+void SdchObserver::RemoveRef() { --reference_count_; }
+
+SdchObserver::~SdchObserver() {
+  // If the reference count is zero, this object is still on an SdchManager's
+  // observer list, and so is dangerous to delete.
+  DCHECK_EQ(0, reference_count_);
+}
+
+}