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 6c7942b237f980b442317913cffe51b832aaa08b..b8eaba4b6327b3d6ddd83722d4bf258dc19bc4b3 100644
--- a/Source/core/page/Page.cpp
+++ b/Source/core/page/Page.cpp
@@ -820,6 +820,23 @@ 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()
     : chromeClient(0)
     , contextMenuClient(0)