Revert of Add gpu implementation of OverdrawXfermode

src/gpu/glsl/GrGLSLXferProcessor.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "glsl/GrGLSLXferProcessor.h"
 
 #include "GrXferProcessor.h"
@@ skipping 70 matching lines @@
         } else {
             SkASSERT(!fDstScaleUni.isValid());
         }
     } else {
         SkASSERT(!fDstTopLeftUni.isValid());
         SkASSERT(!fDstScaleUni.isValid());
     }
     this->onSetData(pdm, xp);
 }
 
-void GrGLSLXferProcessor::DefaultCoverageModulation(GrGLSLXPFragmentBuilder* fragBuilder,
-                                                    const char* srcCoverage,
-                                                    const char* dstColor,
-                                                    const char* outColor,
-                                                    const char* outColorSecondary,
-                                                    const GrXferProcessor& proc) {
-    if (proc.dstReadUsesMixedSamples()) {
-        if (srcCoverage) {
-            fragBuilder->codeAppendf("%s *= %s;", outColor, srcCoverage);
-            fragBuilder->codeAppendf("%s = %s;", outColorSecondary, srcCoverage);
-        } else {
-            fragBuilder->codeAppendf("%s = vec4(1.0);", outColorSecondary);
-        }
-    } else if (srcCoverage) {
-        fragBuilder->codeAppendf("%s = %s * %s + (vec4(1.0) - %s) * %s;",
-                                 outColor, srcCoverage, outColor, srcCoverage, dstColor);
-    }
-}