Rename gl_SampleMask to sk_SampleMask

Change-Id: I3924c6f76edf310a984e4fd89478b00eeec69722
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249931
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
diff --git a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
index 85dc827..7402464 100644
--- a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
+++ b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
@@ -105,15 +105,15 @@
     if (!fHasModifiedSampleMask) {
         fHasModifiedSampleMask = true;
         if (ScopeFlags::kTopLevel != scopeFlags) {
-            this->codePrependf("gl_SampleMask[0] = ~0;");
+            this->codePrependf("sk_SampleMask[0] = ~0;");
         }
         if (!(ScopeFlags::kInsideLoop & scopeFlags)) {
-            this->codeAppendf("gl_SampleMask[0] = (%s);", mask);
+            this->codeAppendf("sk_SampleMask[0] = (%s);", mask);
             return;
         }
     }
 
-    this->codeAppendf("gl_SampleMask[0] &= (%s);", mask);
+    this->codeAppendf("sk_SampleMask[0] &= (%s);", mask);
 }
 
 void GrGLSLFragmentShaderBuilder::applyFnToMultisampleMask(