Lazy init batch unique ID

src/gpu/batches/GrBatch.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrBatch_DEFINED
 #define GrBatch_DEFINED
 
@@ skipping 77 matching lines @@
         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; }
 
-#if GR_BATCH_SPEW
-    uint32_t uniqueID() const { return fUniqueID; }
-#endif
+    uint32_t uniqueID() const { 

[bsalomon, 2016/03/08 16:38:35]

Maybe a comment that we lazily initialize because we don't typically use the
uniqueID() other than for audit trail?

+        if (kIllegalBatchID == fUniqueID) {
+            fUniqueID = GenBatchID();
+        }
+        return fUniqueID; 
+    }
     SkDEBUGCODE(bool isUsed() const { return fUsed; })
 
     /** Called prior to drawing. The batch should perform any resource creation necessary to
         to quickly issue its draw when draw is called. */
     void prepare(GrBatchFlushState* state) { this->onPrepare(state); }
 
     /** Issues the batches commands to GrGpu. */
     void draw(GrBatchFlushState* state) { this->onDraw(state); }
 
     /** Used to block batching across render target changes. Remove this once we store
@@ skipping 35 matching lines @@
         }
         return id;
     }
 
     enum {
         kIllegalBatchID = 0,
     };
 
     SkDEBUGCODE(bool                    fUsed;)
     const uint32_t                      fClassID;
-#if GR_BATCH_SPEW
     static uint32_t GenBatchID() { return GenID(&gCurrBatchUniqueID); }
-    const uint32_t                      fUniqueID;
+    mutable uint32_t                    fUniqueID;
     static int32_t                      gCurrBatchUniqueID;
-#endif
     static int32_t                      gCurrBatchClassID;
 };
 
 #endif