Lose/restore WebGL contexts if multisampling blackist status changes at runtime.

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 808 matching lines @@
     info.ignoreMember(m_plugInClient);
     info.ignoreMember(m_validationMessageClient);
 }
 
 void Page::captionPreferencesChanged()
 {
     for (Frame* frame = mainFrame(); frame; frame = frame->tree()->traverseNext())
         frame->document()->captionPreferencesChanged();
 }
 
+Page::MultisamplingChangedObserver::MultisamplingChangedObserver(Page* page)
+    : m_page(page)
+{
+    m_page->m_multisamplingChangedObservers.add(this);
+}
+
+Page::MultisamplingChangedObserver::~MultisamplingChangedObserver()
+{
+    m_page->m_multisamplingChangedObservers.remove(this);
+}

[Ken Russell (switch to Gerrit), 2013/05/08 02:17:02]

It's confusing to me that the base class MultisamplingChangedObserver adds and
removes itself from the Page's hash set. I would recommend instead making
MultisamplingChangedObserver a pure virtual class with a single method, add
add/removeMultisamplingChangedObserver methods to Page, and just make
WebGLRenderingContext itself implement MultisamplingChangedObserver, and remove
itself from the Page's set in its destructor (since Page outlives
WebGLRenderingContext).

+
+void Page::multisamplingChanged()
+{
+    HashSet<MultisamplingChangedObserver*>::iterator stop = m_multisamplingChangedObservers.end();
+    for (HashSet<MultisamplingChangedObserver*>::iterator it = m_multisamplingChangedObservers.begin(); it != stop; ++it)
+        (*it)->multisamplingChanged(m_settings->openGLMultisamplingEnabled());

[abarth-chromium, 2013/05/07 22:10:59]

Can this call end up executing JavaScript or destroying the Page?

[Ken Russell (switch to Gerrit), 2013/05/08 02:17:02]

Actually, it's guaranteed that it doesn't. It starts a timer which dispatches an
event to JavaScript.

+}
+
 Page::PageClients::PageClients()
     : alternativeTextClient(0)
     , chromeClient(0)
     , contextMenuClient(0)
     , editorClient(0)
     , dragClient(0)
     , inspectorClient(0)
     , plugInClient(0)
 {
 }
 
 Page::PageClients::~PageClients()
 {
 }
 
 } // namespace WebCore