Add a callback for when a gl functor is released

Bug: 27709981

Change-Id: Id5be3e8f88d6d84a9c59c7ed23e7e8862feefbe8
diff --git a/libs/hwui/RenderNode.cpp b/libs/hwui/RenderNode.cpp
index ea06fcd..6e848fd 100644
--- a/libs/hwui/RenderNode.cpp
+++ b/libs/hwui/RenderNode.cpp
@@ -474,8 +474,8 @@
     mDisplayList = mStagingDisplayList;
     mStagingDisplayList = nullptr;
     if (mDisplayList) {
-        for (size_t i = 0; i < mDisplayList->getFunctors().size(); i++) {
-            (*mDisplayList->getFunctors()[i])(DrawGlInfo::kModeSync, nullptr);
+        for (auto& iter : mDisplayList->getFunctors()) {
+            (*iter.functor)(DrawGlInfo::kModeSync, nullptr);
         }
         for (size_t i = 0; i < mDisplayList->getPushStagingFunctors().size(); i++) {
             (*mDisplayList->getPushStagingFunctors()[i])();