command_buffer: Implement CHROMIUM_framebuffer_mixed_samples extension

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 1192 matching lines @@
                                                      const GLchar* name);
 
 #define GL_SRC_ALPHA_SATURATE_EXT 0x0308
 #define GL_SRC1_ALPHA_EXT 0x8589  // OpenGL 1.5 token value
 #define GL_SRC1_COLOR_EXT 0x88F9
 #define GL_ONE_MINUS_SRC1_COLOR_EXT 0x88FA
 #define GL_ONE_MINUS_SRC1_ALPHA_EXT 0x88FB
 #define GL_MAX_DUAL_SOURCE_DRAW_BUFFERS_EXT 0x88FC
 #endif /* GL_EXT_blend_func_extended */
 
+#ifndef GL_CHROMIUM_framebuffer_mixed_samples
+#define GL_CHROMIUM_framebuffer_mixed_samples 1
+typedef void(GL_APIENTRYP PFNGLCOVERAGEMODULATIONCHROMIUMPROC)(
+    GLenum components);
+#ifdef GL_GLEXT_PROTOTYPES
+GL_APICALL void GL_APIENTRY glCoverageModulationCHROMIUM(GLenum components);
+#endif
+#define GL_COVERAGE_MODULATION_CHROMIUM 0x9332
+#endif /* GL_CHROMIUM_framebuffer_mixed_samples */
+
 #ifdef __cplusplus
 }
 #endif
 
 #endif  // GPU_GLES2_GL2EXTCHROMIUM_H_