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

Source/core/platform/graphics/gpu/DrawingBuffer.cpp

Index: Source/core/platform/graphics/gpu/DrawingBuffer.cpp
diff --git a/Source/core/platform/graphics/gpu/DrawingBuffer.cpp b/Source/core/platform/graphics/gpu/DrawingBuffer.cpp
index a2c3725bfae6d0697911d1d6c6271e50a3d7bb56..9ba8e5b3c264eaba03c1b987d0ac92bc789be822 100644
--- a/Source/core/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/Source/core/platform/graphics/gpu/DrawingBuffer.cpp
@@ -83,8 +83,7 @@ private:
 PassRefPtr<DrawingBuffer> DrawingBuffer::create(GraphicsContext3D* context, const IntSize& size, PreserveDrawingBuffer preserve, PassRefPtr<ContextEvictionManager> contextEvictionManager)
 {
     Extensions3D* extensions = context->getExtensions();
-    bool multisampleSupported = extensions->maySupportMultisampling()
-        && extensions->supports("GL_ANGLE_framebuffer_blit")
+    bool multisampleSupported = extensions->supports("GL_ANGLE_framebuffer_blit")
         && extensions->supports("GL_ANGLE_framebuffer_multisample")
         && extensions->supports("GL_OES_rgb8_rgba8");
     if (multisampleSupported) {