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

Source/core/page/Settings.h

Index: Source/core/page/Settings.h
diff --git a/Source/core/page/Settings.h b/Source/core/page/Settings.h
index 5a6b3db18f502c07fbdb0d24b49867618437b475..3cd5b616170c1a356d3484151da0c1bbff7e11d4 100644
--- a/Source/core/page/Settings.h
+++ b/Source/core/page/Settings.h
@@ -160,6 +160,9 @@ namespace WebCore {
         void setTouchEventEmulationEnabled(bool enabled) { m_touchEventEmulationEnabled = enabled; }
         bool isTouchEventEmulationEnabled() const { return m_touchEventEmulationEnabled; }
 
+        void setOpenGLMultisamplingEnabled(bool flag);
+        bool openGLMultisamplingEnabled();
+
     private:
         explicit Settings(Page*);
 
@@ -195,6 +198,7 @@ namespace WebCore {
         bool m_dnsPrefetchingEnabled : 1;
 
         bool m_touchEventEmulationEnabled : 1;
+        bool m_openGLMultisamplingEnabled : 1;
 
         Timer<Settings> m_setImageLoadingSettingsTimer;
         void imageLoadingSettingsTimerFired(Timer<Settings>*);