Reland of add a ClassID function to GrBatch

src/gpu/batches/GrBatch.h

Index: src/gpu/batches/GrBatch.h
diff --git a/src/gpu/batches/GrBatch.h b/src/gpu/batches/GrBatch.h
index b6eec1f969ea1e25de8eb4c86946882a8efa2ba4..c5fc80c5d50dfbd622dfb69e3eb9adfbcd3c31f9 100644
--- a/src/gpu/batches/GrBatch.h
+++ b/src/gpu/batches/GrBatch.h
@@ -41,9 +41,16 @@
     #define GrBATCH_INFO(...)
 #endif
 
+// A helper macro to generate a class static id
+#define DEFINE_BATCH_CLASS_ID \
+    static uint32_t ClassID() { \
+        static uint32_t kClassID = GenBatchClassID(); \
+        return kClassID; \
+    }
+
 class GrBatch : public GrNonAtomicRef {
 public:
-    GrBatch();
+    GrBatch(uint32_t classID);
     ~GrBatch() override;
 
     virtual const char* name() const = 0;
@@ -69,10 +76,17 @@
     }
 
     /**
-     * Helper for down-casting to a GrBatch subclass
+     * Helper for safely down-casting to a GrBatch subclass
      */
-    template <typename T> const T& cast() const { return *static_cast<const T*>(this); }
-    template <typename T> T* cast() { return static_cast<T*>(this); }
+    template <typename T> const T& cast() const {
+        SkASSERT(T::ClassID() == this->classID());
+        return *static_cast<const T*>(this);
+    }
+
+    template <typename T> T* cast() {
+        SkASSERT(T::ClassID() == this->classID());
+        return static_cast<T*>(this);
+    }
 
     uint32_t classID() const { SkASSERT(kIllegalBatchID != fClassID); return fClassID; }
 
@@ -96,11 +110,6 @@
     virtual SkString dumpInfo() const = 0;
 
 protected:
-    template <typename PROC_SUBCLASS> void initClassID() {
-         static uint32_t kClassID = GenID(&gCurrBatchClassID);
-         fClassID = kClassID;
-    }
-
     // NOTE, compute some bounds, even if extremely conservative.  Do *NOT* setLargest on the bounds
     // rect because we outset it for dst copy textures
     void setBounds(const SkRect& newBounds) { fBounds = newBounds; }
@@ -108,6 +117,8 @@
     void joinBounds(const SkRect& otherBounds) {
         return fBounds.joinPossiblyEmptyRect(otherBounds);
     }
+
+    static uint32_t GenBatchClassID() { return GenID(&gCurrBatchClassID); }
 
     SkRect                              fBounds;
 
@@ -118,8 +129,7 @@
     virtual void onDraw(GrBatchFlushState*) = 0;
 
     static uint32_t GenID(int32_t* idCounter) {
-        // fCurrProcessorClassID has been initialized to kIllegalProcessorClassID. The
-        // atomic inc returns the old value not the incremented value. So we add
+        // The atomic inc returns the old value not the incremented value. So we add
         // 1 to the returned value.
         uint32_t id = static_cast<uint32_t>(sk_atomic_inc(idCounter)) + 1;
         if (!id) {
@@ -133,13 +143,14 @@
         kIllegalBatchID = 0,
     };
 
-    uint32_t                            fClassID;
     SkDEBUGCODE(bool                    fUsed;)
+    const uint32_t                      fClassID;
 #if GR_BATCH_SPEW
-    uint32_t                            fUniqueID;
-    static int32_t gCurrBatchUniqueID;
+    static uint32_t GenBatchID() { return GenID(&gCurrBatchUniqueID); }
+    const uint32_t                      fUniqueID;
+    static int32_t                      gCurrBatchUniqueID;
 #endif
-    static int32_t gCurrBatchClassID;
+    static int32_t                      gCurrBatchClassID;
     typedef GrNonAtomicRef INHERITED;
 };