Implement support for KHR_blend_equation_advanced

src/gpu/gl/GrGLCaps.cpp

Index: src/gpu/gl/GrGLCaps.cpp
diff --git a/src/gpu/gl/GrGLCaps.cpp b/src/gpu/gl/GrGLCaps.cpp
index 73bf6f0ee6aaf6fc2a0e90dfcc572ed49e0cce48..b0634a16646aafdb0589a97b6f1d6eb45b0a3e1e 100644
--- a/src/gpu/gl/GrGLCaps.cpp
+++ b/src/gpu/gl/GrGLCaps.cpp
@@ -306,6 +306,19 @@ bool GrGLCaps::init(const GrGLContextInfo& ctxInfo, const GrGLInterface* gli) {
         fStencilWrapOpsSupport = true;
     }
 
+    // GL_KHR_blend_equation_advanced is a proper subset of GL_NV_blend_equation_advanced, with all
+    // the same enums, but we still check for the NV variants to support legacy drivers that didn't
+    // export the KHR extension yet.
+    if (ctxInfo.hasExtension("GL_KHR_blend_equation_advanced_coherent") ||
+        ctxInfo.hasExtension("GL_NV_blend_equation_advanced_coherent")) {
+        fBlendEquationSupport = kAdvancedCoherent_BlendEquationSupport;
+    } else if (ctxInfo.hasExtension("GL_KHR_blend_equation_advanced") ||
+               ctxInfo.hasExtension("GL_NV_blend_equation_advanced")) {
+        fBlendEquationSupport = kAdvanced_BlendEquationSupport;
+    } else {
+        fBlendEquationSupport = kBasic_BlendEquationSupport;
+    }
+
     if (kGL_GrGLStandard == standard) {
         fMapBufferFlags = kCanMap_MapFlag; // we require VBO support and the desktop VBO
                                             // extension includes glMapBuffer.