Detach SpeechRecognitionController upon page detach.

Source/core/page/Page.cpp

Index: Source/core/page/Page.cpp
diff --git a/Source/core/page/Page.cpp b/Source/core/page/Page.cpp
index ed22d5b087d8e955b7f9412e52500df60af7ab18..7559876f6750e59213bd506d88a84c9d97630a76 100644
--- a/Source/core/page/Page.cpp
+++ b/Source/core/page/Page.cpp
@@ -610,6 +610,7 @@ void Page::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()