Revert of Move DstCopy on gpu into the GrXferProcessor.

src/gpu/GrProgramDesc.h

Index: src/gpu/GrProgramDesc.h
diff --git a/src/gpu/GrProgramDesc.h b/src/gpu/GrProgramDesc.h
index 66e0e06b8c88ed629c1ba7eeb06c795923895ce7..e07e116733b8a5313402d00fa0c7595c481fcef3 100644
--- a/src/gpu/GrProgramDesc.h
+++ b/src/gpu/GrProgramDesc.h
@@ -55,6 +55,9 @@
     }
 
     struct KeyHeader {
+        uint8_t                     fDstReadKey;   // set by GrGLShaderBuilder if there
+                                                   // are effects that must read the dst.
+                                                   // Otherwise, 0.
         uint8_t                     fFragPosKey;   // set by GrGLShaderBuilder if there are
                                                    // effects that read the fragment position.
                                                    // Otherwise, 0.
@@ -75,6 +78,20 @@
 
     // This should really only be used internally, base classes should return their own headers
     const KeyHeader& header() const { return *this->atOffset<KeyHeader, kHeaderOffset>(); }
+
+    // A struct to communicate descriptor information to the program descriptor builder
+    struct DescInfo {
+        bool operator==(const DescInfo& that) const {
+            return fReadsDst == that.fReadsDst &&
+                   fReadsFragPosition == that.fReadsFragPosition;
+        }
+        bool operator!=(const DescInfo& that) const { return !(*this == that); };
+
+        // These flags give aggregated info on the processor stages that are used when building
+        // programs.
+        bool            fReadsDst;
+        bool            fReadsFragPosition;
+    };
 
 private:
     template<typename T, size_t OFFSET> T* atOffset() {