Only discard for XP dstCopies if we have a coverage value.

src/gpu/GrXferProcessor.cpp

Index: src/gpu/GrXferProcessor.cpp
diff --git a/src/gpu/GrXferProcessor.cpp b/src/gpu/GrXferProcessor.cpp
index 243b9feb3f32edd6cee2386aaf10d91fb135f89b..bc79b2dbe1a3ea71c895a33a2886d6b91b57c899 100644
--- a/src/gpu/GrXferProcessor.cpp
+++ b/src/gpu/GrXferProcessor.cpp
@@ -8,11 +8,13 @@
 #include "GrXferProcessor.h"
 #include "gl/GrGLCaps.h"
 
-GrXferProcessor::GrXferProcessor() : fWillReadDstColor(false), fDstCopyTextureOffset() {
+GrXferProcessor::GrXferProcessor()
+    : fWillReadDstColor(false), fReadsCoverage(true), fDstCopyTextureOffset() {
 }
 
 GrXferProcessor::GrXferProcessor(const GrDeviceCoordTexture* dstCopy, bool willReadDstColor)
     : fWillReadDstColor(willReadDstColor)
+    , fReadsCoverage(true)
     , fDstCopyTextureOffset() {
     if (dstCopy && dstCopy->texture()) {
         fDstCopy.reset(dstCopy->texture());
@@ -22,6 +24,23 @@ GrXferProcessor::GrXferProcessor(const GrDeviceCoordTexture* dstCopy, bool willR
     }
 }
 
+GrXferProcessor::OptFlags GrXferProcessor::getOptimizations(const GrProcOptInfo& colorPOI,
+                                                            const GrProcOptInfo& coveragePOI,
+                                                            bool doesStencilWrite,
+                                                            GrColor* overrideColor,
+                                                            const GrDrawTargetCaps& caps) {
+    GrXferProcessor::OptFlags flags = this->onGetOptimizations(colorPOI,
+                                                               coveragePOI,
+                                                               doesStencilWrite,
+                                                               overrideColor,
+                                                               caps);
+
+    if (flags & GrXferProcessor::kIgnoreCoverage_OptFlag) {
+        fReadsCoverage = false;
+    }
+    return flags;
+}
+
 void GrXferProcessor::getGLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const {
     uint32_t key = this->willReadDstColor() ? 0x1 : 0x0;
     if (this->getDstCopyTexture() &&