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.

[Ryan Sleevi, 2014/10/20 22:42:04]

I'd rather be explicit and force classes to consume/ignore notifications. This
is in keeping in line with our avoidance of impl-inheritence.

[Randy Smith (Not in Mondays), 2014/10/21 19:05:36]

Define "our"?  This pattern is all through the content API.  (More detail in
other comment on this issue.)

(Which translates to "Ok, but tell me one more time just so I know you've read
the counter-argument; I don't have strong feelings.")

[Ryan Sleevi, 2014/10/21 23:09:29]

See
http://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Multiple_Inhe...
and then the definition of "Pure Interface" in
http://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Interfaces

[Randy Smith (Not in Mondays), 2014/10/23 20:57:07]

Done.

+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_);
+}
+
+}