Add support for all blendmodes if we have GL_KHR_blend_equation_advanced.

BUG=243223

Review URL: https://codereview.chromium.org/643373003

Cr-Commit-Position: refs/heads/master@{#300887}
diff --git a/gpu/command_buffer/cmd_buffer_functions.txt b/gpu/command_buffer/cmd_buffer_functions.txt
index 49cb4339..37c33be0 100644
--- a/gpu/command_buffer/cmd_buffer_functions.txt
+++ b/gpu/command_buffer/cmd_buffer_functions.txt
@@ -222,3 +222,5 @@
 GL_APICALL void         GL_APIENTRY glMatrixLoadfCHROMIUM (GLenumMatrixMode matrixMode, const GLfloat* m);
 GL_APICALL void         GL_APIENTRY glMatrixLoadIdentityCHROMIUM (GLenumMatrixMode matrixMode);
 
+// Extension KHR_blend_equation_advanced
+GL_APICALL void GL_APIENTRY glBlendBarrierKHR (void);