create and thread batch tracker object

src/gpu/GrGeometryProcessor.h

Index: src/gpu/GrGeometryProcessor.h
diff --git a/src/gpu/GrGeometryProcessor.h b/src/gpu/GrGeometryProcessor.h
index 17344d2bb4c251df6469aff20512bb4ba98fdf13..27383a4df49df6dd3e618f24f72fed5a5e745a1d 100644
--- a/src/gpu/GrGeometryProcessor.h
+++ b/src/gpu/GrGeometryProcessor.h
@@ -12,6 +12,30 @@
 #include "GrProcessor.h"
 #include "GrShaderVar.h"
 
+/*
+ * A struct for tracking batching decisions.  While this lives on GrOptState, it is managed
+ * entirely by the derived classes of the GP.
+ */
+class GrBatchTracker {
+public:
+    template <typename T> const T& cast() const {
+        SkASSERT(sizeof(T) <= kMaxSize);
+        return *reinterpret_cast<const T*>(fData);
+    }
+
+    template <typename T> T* cast() {
+        SkASSERT(sizeof(T) <= kMaxSize);
+        return reinterpret_cast<T*>(fData);
+    }
+
+    static const size_t kMaxSize = 32;
+
+private:
+    uint8_t fData[kMaxSize];
+};
+
+class GrOptDrawState;
+
 /**
  * A GrGeometryProcessor is used to perform computation in the vertex shader and
  * add support for custom vertex attributes. A GrGemeotryProcessor is typically
@@ -73,6 +97,15 @@ public:
         return this->onIsEqual(that);
     }
 
+    struct InitBT {
+        bool fOutputColor;
+        bool fOutputCoverage;
+        GrColor fColor;
+        GrColor fCoverage;
+    };
+
+    virtual void initBatchTracker(GrBatchTracker*, const InitBT&) const {}
+
     // TODO this is a total hack until the gp can own whether or not it uses uniform
     // color / coverage
     bool hasVertexColor() const { return fHasVertexColor; }