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..37bca35633b151e70215bfeae5c13f16f8106840 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::addMultisamplingChangedObserver(MultisamplingChangedObserver* observer)
+{
+    m_multisamplingChangedObservers.add(observer);
+}
+
+void Page::removeMultisamplingChangedObserver(MultisamplingChangedObserver* observer)
+{
+    m_multisamplingChangedObservers.remove(observer);
+}
+
+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());
+}
+
 Page::PageClients::PageClients()
     : alternativeTextClient(0)
     , chromeClient(0)