Convert child FPs from refs to pending executions when parent converts

include/gpu/GrProgramElement.h

Index: include/gpu/GrProgramElement.h
diff --git a/include/gpu/GrProgramElement.h b/include/gpu/GrProgramElement.h
index e788486b5cc74d0d4c898268d7754d3e3628b3ac..c71e2074fc41a9cf2c94d517a1142aa2f96a9959 100644
--- a/include/gpu/GrProgramElement.h
+++ b/include/gpu/GrProgramElement.h
@@ -44,6 +44,7 @@ public:
         this->validate();
         --fRefCnt;
         if (0 == fRefCnt) {
+            this->notifyRefCntIsZero();
             if (0 == fPendingExecutions) {
                 delete this;
                 return;
@@ -78,9 +79,6 @@ protected:
         fGpuResources.push_back(res);
     }
 
-private:
-    static uint32_t CreateUniqueID();
-
     void addPendingExecution() const {
         this->validate();
         SkASSERT(fRefCnt > 0);
@@ -105,6 +103,13 @@ private:
         this->validate();
     }
 
+private:
+    /** This will be called when the ref cnt is zero. The object may or may not have pending
+        executions. */
+    virtual void notifyRefCntIsZero() const = 0;
+
+    static uint32_t CreateUniqueID();
+
     void removeRefs() const;
     void addPendingIOs() const;
     void pendingIOComplete() const;