Detach SpeechRecognitionController upon page detach.

Source/core/page/Page.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All Rights Reserved.
  * Copyright (C) 2008 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 592 matching lines @@
 #ifndef NDEBUG
     pageCounter.decrement();
 #endif
 
     m_chrome->willBeDestroyed();
     if (m_validationMessageClient)
         m_validationMessageClient->willBeDestroyed();
     m_mainFrame = nullptr;
 
     Page::notifyContextDestroyed();
+    Page::detachObservers();

[haraken, 2015/02/26 16:29:05]

Hmm, I might want to avoid introducing another lifecycle notification (if
possible).

What happens if we do something like:

for (Observer* observer : m_observers) {
  observer->contextDestroyed();
}
for (Observer* observer : m_observers) {
  observer->clearLifecycleContext();
}

in notifyContextDestroyed()?

[sof, 2015/02/26 17:01:22]

Yes, the explicit clearing here is not without problems, I've now realized -- if
we clear the observer references when detaching the page, then observer
destructors won't be able to unobserve their contexts when they're destructing.
With fatal consequences.

So, needs more work & thought. Leaning towards relying on
FrameDestructionObserver for SpeechRecognitionController instead.

 }
 
 Page::PageClients::PageClients()
     : chromeClient(nullptr)
     , contextMenuClient(nullptr)
     , editorClient(nullptr)
     , dragClient(nullptr)
     , inspectorClient(nullptr)
     , spellCheckerClient(nullptr)
 {
 }
 
 Page::PageClients::~PageClients()
 {
 }
 
 } // namespace blink