Create a static instances of SrcOver XferProcessor

src/gpu/GrXferProcessor.cpp

Index: src/gpu/GrXferProcessor.cpp
diff --git a/src/gpu/GrXferProcessor.cpp b/src/gpu/GrXferProcessor.cpp
index 655fdfae7b0b69002ef444a3ed753cd26958b198..e8a3490c408a3e07920fa953a0f0fa706c8c84a6 100644
--- a/src/gpu/GrXferProcessor.cpp
+++ b/src/gpu/GrXferProcessor.cpp
@@ -13,7 +13,6 @@
 GrXferProcessor::GrXferProcessor()
     : fWillReadDstColor(false)
     , fDstReadUsesMixedSamples(false)
-    , fReadsCoverage(true)
     , fDstTextureOffset() {
 }
 
@@ -22,7 +21,6 @@ GrXferProcessor::GrXferProcessor(const DstTexture* dstTexture,
                                  bool hasMixedSamples)
     : fWillReadDstColor(willReadDstColor)
     , fDstReadUsesMixedSamples(willReadDstColor && hasMixedSamples)
-    , fReadsCoverage(true)
     , fDstTextureOffset() {
     if (dstTexture && dstTexture->texture()) {
         SkASSERT(willReadDstColor);
@@ -37,7 +35,7 @@ GrXferProcessor::OptFlags GrXferProcessor::getOptimizations(const GrProcOptInfo&
                                                             const GrProcOptInfo& coveragePOI,
                                                             bool doesStencilWrite,
                                                             GrColor* overrideColor,
-                                                            const GrCaps& caps) {
+                                                            const GrCaps& caps) const {
     GrXferProcessor::OptFlags flags = this->onGetOptimizations(colorPOI,
                                                                coveragePOI,
                                                                doesStencilWrite,
@@ -51,9 +49,6 @@ GrXferProcessor::OptFlags GrXferProcessor::getOptimizations(const GrProcOptInfo&
             flags |= GrXferProcessor::kIgnoreCoverage_OptFlag;
         }
     }
-    if (flags & GrXferProcessor::kIgnoreCoverage_OptFlag) {
-        fReadsCoverage = false;
-    }
     return flags;
 }
 
@@ -82,11 +77,8 @@ void GrXferProcessor::getGLSLProcessorKey(const GrGLSLCaps& caps, GrProcessorKey
                 key |= 0x4;
             }
         }
-        if (this->readsCoverage()) {
-            key |= 0x8;
-        }
         if (this->dstReadUsesMixedSamples()) {
-            key |= 0x10;
+            key |= 0x8;
         }
     }
     b->add32(key);