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 7ef12c80fd873454a40ddfbf68988d005cf6485d..c86f6ee5cf4aa00dfca56777caab097fcec612a3 100644
--- a/Source/core/page/Settings.h
+++ b/Source/core/page/Settings.h
@@ -160,6 +160,9 @@ public:
     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 @@ private:
     bool m_dnsPrefetchingEnabled : 1;
 
     bool m_touchEventEmulationEnabled : 1;
+    bool m_openGLMultisamplingEnabled : 1;
 
     Timer<Settings> m_setImageLoadingSettingsTimer;
     void imageLoadingSettingsTimerFired(Timer<Settings>*);