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

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 8296aa459215a3794cdff5acb962abd45b108b18..c883a04be9bfe86f5a3bfbd33be81b174e7e82bd 100644
--- a/Source/core/page/Page.cpp
+++ b/Source/core/page/Page.cpp
@@ -826,6 +826,23 @@ void Page::captionPreferencesChanged()
         frame->document()->captionPreferencesChanged();
 }
 
+void Page::addSettingsChangedObserver(SettingsChangedObserver* observer)
+{
+    m_settingsChangedObservers.add(observer);
+}
+
+void Page::removeSettingsChangedObserver(SettingsChangedObserver* observer)
+{
+    m_settingsChangedObservers.remove(observer);
+}
+
+void Page::settingsChanged() const
+{
+    HashSet<SettingsChangedObserver*>::iterator stop = m_settingsChangedObservers.end();
+    for (HashSet<SettingsChangedObserver*>::iterator it = m_settingsChangedObservers.begin(); it != stop; ++it)
+        (*it)->settingsChanged(m_settings.get());

[abarth-chromium, 2013/05/06 21:58:30]

This is a weak iteration pattern.  What if calling settingsChanged mutates
m_settingsChangedObservers?

+}
+
 Page::PageClients::PageClients()
     : alternativeTextClient(0)
     , chromeClient(0)