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

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

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 65 matching lines @@
 
 private:
     GraphicsContext3D* m_context;
     GC3Denum m_oldActiveTextureUnit;
     Platform3DObject m_oldTextureUnitZeroId;
 };
 
 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) {
         extensions->ensureEnabled("GL_ANGLE_framebuffer_blit");
         extensions->ensureEnabled("GL_ANGLE_framebuffer_multisample");
         extensions->ensureEnabled("GL_OES_rgb8_rgba8");
     }
     bool packedDepthStencilSupported = extensions->supports("GL_OES_packed_depth_stencil");
     if (packedDepthStencilSupported)
         extensions->ensureEnabled("GL_OES_packed_depth_stencil");
@@ skipping 720 matching lines @@
 
 void DrawingBuffer::bind()
 {
     if (!m_context)
         return;
 
     m_context->bindFramebuffer(GraphicsContext3D::FRAMEBUFFER, m_multisampleFBO ? m_multisampleFBO : m_fbo);
 }
 
 } // namespace WebCore