Add GL_CHROMIUM_screen_space_antialiasing to support alternative AA

Source/platform/graphics/gpu/DrawingBuffer.h

 /*
  * 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 162 matching lines @@
     // Destroys the TEXTURE_2D binding for the owned context
     bool copyToPlatformTexture(WebGraphicsContext3D*, Platform3DObject texture, GLenum internalFormat,
         GLenum destType, GLint level, bool premultiplyAlpha, bool flipY, SourceDrawingBuffer);
 
     void setPackAlignment(GLint param);
 
     void paintRenderingResultsToCanvas(ImageBuffer*);
     bool paintRenderingResultsToImageData(int&, int&, SourceDrawingBuffer, WTF::ArrayBufferContents&);
 
     int sampleCount() const { return m_sampleCount; }
-    bool explicitResolveOfMultisampleData() const { return m_multisampleMode == ExplicitResolve; }
+    bool explicitResolveOfMultisampleData() const { return m_antiAliasingMode == MSAAExplicitResolve; }
 
     // Bind to m_drawFramebufferBinding or m_readFramebufferBinding if it's not 0.
     // Otherwise, bind to the default FBO.
     void restoreFramebufferBindings();
 
 protected: // For unittests
     DrawingBuffer(
         PassOwnPtr<WebGraphicsContext3D>,
         PassOwnPtr<Extensions3DUtil>,
         bool multisampleExtensionSupported,
@@ skipping 80 matching lines @@
     Platform3DObject m_multisampleFBO;
     Platform3DObject m_multisampleColorBuffer;
 
     // True if our contents have been modified since the last presentation of this buffer.
     bool m_contentsChanged;
 
     // True if commit() has been called since the last time markContentsChanged() had been called.
     bool m_contentsChangeCommitted;
     bool m_bufferClearNeeded;
 
-    enum MultisampleMode {
+    enum AntialiasingMode {
         None,
-        ImplicitResolve,
-        ExplicitResolve,
+        MSAAImplicitResolve,
+        MSAAExplicitResolve,
+        ScreenSpaceAntialiasing,
     };
 
-    MultisampleMode m_multisampleMode;
+    AntialiasingMode m_antiAliasingMode;
 
     WebGraphicsContext3D::Attributes m_actualAttributes;
     unsigned m_internalColorFormat;
     unsigned m_colorFormat;
     unsigned m_internalRenderbufferFormat;
     int m_maxTextureSize;
     int m_sampleCount;
     int m_packAlignment;
     bool m_destructionInProgress;
     bool m_isHidden;
@@ skipping 13 matching lines @@
     // used to resize the Canvas.
     SkBitmap m_resizingBitmap;
 
     // Used to flip a bitmap vertically.
     Vector<uint8_t> m_scanline;
 };
 
 } // namespace blink
 
 #endif // DrawingBuffer_h