Add GL_CHROMIUM_screen_space_antialiasing to support alternative AA

gpu/blink/webgraphicscontext3d_impl.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef GPU_BLINK_WEBGRAPHICSCONTEXT3D_IMPL_H_
 #define GPU_BLINK_WEBGRAPHICSCONTEXT3D_IMPL_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 32 matching lines @@
   virtual void loseContextCHROMIUM(blink::WGC3Denum current,
                                    blink::WGC3Denum other);
 
   virtual void reshapeWithScaleFactor(
       int width, int height, float scale_factor);
 
   virtual void prepareTexture();
   virtual void postSubBufferCHROMIUM(int x, int y, int width, int height);
 
   virtual void activeTexture(blink::WGC3Denum texture);
+  virtual void applyScreenSpaceAntialiasingCHROMIUM();
   virtual void attachShader(blink::WebGLId program, blink::WebGLId shader);
   virtual void bindAttribLocation(blink::WebGLId program,
                                   blink::WGC3Duint index,
                                   const blink::WGC3Dchar* name);
   virtual void bindBuffer(blink::WGC3Denum target, blink::WebGLId buffer);
   virtual void bindFramebuffer(blink::WGC3Denum target,
                                blink::WebGLId framebuffer);
   virtual void bindRenderbuffer(blink::WGC3Denum target,
                                 blink::WebGLId renderbuffer);
   virtual void bindTexture(blink::WGC3Denum target, blink::WebGLId texture);
@@ skipping 897 matching lines @@
   std::vector<blink::WGC3Denum> synthetic_errors_;
 
   ::gpu::gles2::GLES2Interface* gl_;
   bool lose_context_when_out_of_memory_;
   uint32_t flush_id_;
 };
 
 }  // namespace gpu_blink
 
 #endif  // GPU_BLINK_WEBGRAPHICSCONTEXT3D_IMPL_H_