Change implementation of flush-count based GrGpuResource purging

src/gpu/GrGpuResourceCacheAccess.h

Index: src/gpu/GrGpuResourceCacheAccess.h
diff --git a/src/gpu/GrGpuResourceCacheAccess.h b/src/gpu/GrGpuResourceCacheAccess.h
index b09dcc1872c6b4133e4746d0d2859814e88b3a55..e91f899cf2b84c7a97145c873ce84e78516b528f 100644
--- a/src/gpu/GrGpuResourceCacheAccess.h
+++ b/src/gpu/GrGpuResourceCacheAccess.h
@@ -58,6 +58,20 @@ private:
     uint32_t timestamp() const { return fResource->fTimestamp; }
     void setTimestamp(uint32_t ts) { fResource->fTimestamp = ts; }
 
+    /** Called by the cache to record when this became purgeable. */
+    void setFlushCntWhenResourceBecamePurgeable(uint32_t cnt) {
+        SkASSERT(fResource->isPurgeable());
+        fResource->fExternalFlushCntWhenBecamePurgeable = cnt;
+    }
+    /**
+     * Called by the cache to determine whether this resource has been puregable for more than
+     * a threshold number of external flushes.
+     */
+    uint32_t flushCntWhenResourceBecamePurgeable() {
+        SkASSERT(fResource->isPurgeable());
+        return fResource->fExternalFlushCntWhenBecamePurgeable;
+    }
+
     int* accessCacheIndex() const { return &fResource->fCacheArrayIndex; }
 
     CacheAccess(GrGpuResource* resource) : fResource(resource) {}