Overhaul RenderNode's DisplayList management

* Move mValid to native
* Have destroyHardwareResources destroy everything
* Remove flaky mParentCount checks in setStaging
* All tree updates have an internal observer to
  ensure onRemovedFromTree() is a reliable signal
* onRemovedFromTree() immediately releases resources
  to avoid displaylist "leaks"

Test: Unit tests for validity added & pass, manually
verified that b/34072929 doesn't repro

Bug: 34072929

Change-Id: I856534b4ed1b7f009fc4b7cd13209b97fa42a71c
diff --git a/libs/hwui/DisplayList.h b/libs/hwui/DisplayList.h
index cab092f..ef0fd31 100644
--- a/libs/hwui/DisplayList.h
+++ b/libs/hwui/DisplayList.h
@@ -125,8 +125,8 @@
 
     virtual void syncContents();
     virtual void updateChildren(std::function<void(RenderNode*)> updateFn);
-    virtual bool prepareListAndChildren(TreeInfo& info, bool functorsNeedLayer,
-            std::function<void(RenderNode*, TreeInfo&, bool)> childFn);
+    virtual bool prepareListAndChildren(TreeObserver& observer, TreeInfo& info, bool functorsNeedLayer,
+            std::function<void(RenderNode*, TreeObserver&, TreeInfo&, bool)> childFn);
 
 protected:
     // allocator into which all ops and LsaVector arrays allocated