Create a static instances of SrcOver XferProcessor

src/gpu/gl/GrGLProgramDesc.cpp

Index: src/gpu/gl/GrGLProgramDesc.cpp
diff --git a/src/gpu/gl/GrGLProgramDesc.cpp b/src/gpu/gl/GrGLProgramDesc.cpp
index e3ee9139c2e027580be17b45a0878cba0ce91e7f..a841c2cf16b24665b8bf64478a9bc9086e363ef7 100644
--- a/src/gpu/gl/GrGLProgramDesc.cpp
+++ b/src/gpu/gl/GrGLProgramDesc.cpp
@@ -147,6 +147,13 @@ bool GrGLProgramDescBuilder::Build(GrProgramDesc* desc,
     } else {
         header->fFragPosKey = 0;
     }
+
+    if (pipeline.readsCoverage()) {
+        header->fReadsCoverage = 1;
+    } else {
+        header->fReadsCoverage = 0;
+    }
+
     header->fSnapVerticesToPixelCenters = pipeline.snapVerticesToPixelCenters();
     header->fColorEffectCnt = pipeline.numColorFragmentProcessors();
     header->fCoverageEffectCnt = pipeline.numCoverageFragmentProcessors();