Remove canTweakAlphaForCoverage from XP's since batch reads flag.

src/gpu/effects/GrPorterDuffXferProcessor.cpp

Index: src/gpu/effects/GrPorterDuffXferProcessor.cpp
diff --git a/src/gpu/effects/GrPorterDuffXferProcessor.cpp b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
index b2c81754a18bae71e2ec61c42724df25d47e9f06..506383a29ea9ce969ab103dd0d5333d4f78e8037 100644
--- a/src/gpu/effects/GrPorterDuffXferProcessor.cpp
+++ b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
@@ -591,10 +591,6 @@ bool GrPorterDuffXPFactory::supportsRGBCoverage(GrColor /*knownColor*/,
     return false;
 }
 
-bool GrPorterDuffXPFactory::canTweakAlphaForCoverage() const {
-    return can_tweak_alpha_for_coverage(fDstCoeff);
-}
-
 void GrPorterDuffXPFactory::getInvariantOutput(const GrProcOptInfo& colorPOI,
                                                const GrProcOptInfo& coveragePOI,
                                                GrXPFactory::InvariantOutput* output) const {
@@ -672,7 +668,7 @@ bool GrPorterDuffXPFactory::willReadDstColor(const GrDrawTargetCaps& caps,
         return false;
     }
 
-    if (this->canTweakAlphaForCoverage()) {
+    if (can_tweak_alpha_for_coverage(fDstCoeff)) {
         return false;
     }