Add a comment for the new CHROMIUM extension.

gpu/GLES2/gl2ext.h

 #ifndef __gl2ext_h_
 #define __gl2ext_h_
 
 /* $Revision: 15049 $ on $Date:: 2011-07-06 17:28:16 -0700 #$ */
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 /*
@@ skipping 1332 matching lines @@
 #define glEnableFeatureCHROMIUM GLES2_GET_FUN(EnableFeatureCHROMIUM)
 #if !defined(GLES2_USE_CPP_BINDINGS)
 GL_APICALL void GL_APIENTRY glEnableFeatureCHROMIUM (const GLchar *feature);
 #endif
 #else
 typedef void (GL_APIENTRYP PFNGLENABLEFEATURECHROMIUM) (const GLchar *feature);
 #endif
 #endif
 
 /* GL_CHROMIUM_post_sub_buffer */
+/* This extension is modeled after EGL_NV_post_sub_buffer and
+ * GLX_MESA_copy_sub_buffer. It's like a SwapBuffers, but it pushes a region
+ * of the back buffer to the front buffer.
+ */
 #ifndef GL_CHROMIUM_post_sub_buffer
 #define GL_CHROMIUM_post_sub_buffer 1
 #ifdef GL_GLEXT_PROTOTYPES
 #define glPostSubBufferCHROMIUM GLES2_GET_FUN(PostSubBufferCHROMIUM)
 #if !defined(GLES2_USE_CPP_BINDINGS)
 GL_APICALL void GL_APIENTRY glPostSubBufferCHROMIUM (GLint x, GLint y, GLint width, GLint height);
 #endif
 #else
 typedef void (GL_APIENTRYP PFNGLPOSTSUBBUFFERCHROMIUM) (GLint x, GLint y, GLint width, GLint height);
 #endif
@@ skipping 32 matching lines @@
 #endif
 #endif
 typedef void (GL_APIENTRYP PFNGLGETTRANSLATEDSHADERSOURCEANGLEPROC) (GLuint shader, GLsizei bufsize, GLsizei* length, GLchar* source);
 #endif
 
 #ifdef __cplusplus
 }
 #endif
 
 #endif /* __gl2ext_h_ */