Add GL_CHROMIUM_screen_space_antialiasing to support alternative AA

gpu/GLES2/gl2extchromium.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.
 
 // This file contains Chromium-specific GLES2 extensions declarations.
 
 #ifndef GPU_GLES2_GL2EXTCHROMIUM_H_
 #define GPU_GLES2_GL2EXTCHROMIUM_H_
 
 #include <GLES2/gl2.h>
@@ skipping 503 matching lines @@
 /* GL_CHROMIUM_command_buffer_latency_query */
 #ifndef GL_CHROMIUM_command_buffer_latency_query
 #define GL_CHROMIUM_command_buffer_latency_query 1
 
 #ifndef GL_LATENCY_QUERY_CHROMIUM
 // TODO(gman): Get official numbers for these constants.
 #define GL_LATENCY_QUERY_CHROMIUM 0x6007
 #endif
 #endif  /* GL_CHROMIUM_command_buffer_latency_query */
 
+/* GL_CHROMIUM_screen_space_antialiasing */
+#ifndef GL_CHROMIUM_screen_space_antialiasing
+#define GL_CHROMIUM_screen_space_antialiasing 1
+#ifdef GL_GLEXT_PROTOTYPES
+GL_APICALL void GL_APIENTRY glApplyScreenSpaceAntialiasingCHROMIUM();
+#endif
+typedef void(GL_APIENTRYP PFNGLAPPLYSCREENSPACEANTIALIASINGCHROMIUMPROC)();
+#endif /* GL_CHROMIUM_screen_space_antialiasing */
+
 /* GL_ARB_robustness */
 #ifndef GL_ARB_robustness
 #define GL_ARB_robustness 1
 
 #ifndef GL_GUILTY_CONTEXT_RESET_ARB
 #define GL_GUILTY_CONTEXT_RESET_ARB 0x8253
 #endif
 
 #ifndef GL_UNKNOWN_CONTEXT_RESET_ARB
 #define GL_UNKNOWN_CONTEXT_RESET_ARB 0x8255
@@ skipping 451 matching lines @@
 #define GL_PATH_STENCIL_VALUE_MASK_CHROMIUM 0x90B9
 #endif
 
 #endif /* GL_CHROMIUM_path_rendering */
 
 #ifdef __cplusplus
 }
 #endif
 
 #endif  // GPU_GLES2_GL2EXTCHROMIUM_H_