Don't ref/unref the static src-over xp
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bug=chromium:570301

Review URL: https://codereview.chromium.org/1540363002
diff --git a/src/gpu/gl/GrGLProgramDesc.cpp b/src/gpu/gl/GrGLProgramDesc.cpp
index e3d292c..81f92eb 100644
--- a/src/gpu/gl/GrGLProgramDesc.cpp
+++ b/src/gpu/gl/GrGLProgramDesc.cpp
@@ -125,7 +125,7 @@
         }
     }
 
-    const GrXferProcessor& xp = *pipeline.getXferProcessor();
+    const GrXferProcessor& xp = pipeline.getXferProcessor();
     xp.getGLSLProcessorKey(*gpu->glCaps().glslCaps(), &b);
     //**** use glslCaps here?
     if (!gen_meta_key(xp, gpu->glCaps(), 0, &b)) {