Add overrides and switch to nullptr keyword for all files

Adds remaining missing overrides and nullptr usages, missed due to
an extreme failure in tool usage.

Change-Id: I56abd72975a3999ad13330003c348db40f59aebf
diff --git a/libs/hwui/tests/main.cpp b/libs/hwui/tests/main.cpp
index 4efef6f..152e7b2 100644
--- a/libs/hwui/tests/main.cpp
+++ b/libs/hwui/tests/main.cpp
@@ -33,7 +33,7 @@
 
 class ContextFactory : public IContextFactory {
 public:
-    virtual AnimationContext* createAnimationContext(renderthread::TimeLord& clock) {
+    virtual AnimationContext* createAnimationContext(renderthread::TimeLord& clock) override {
         return new AnimationContext(clock);
     }
 };
@@ -76,7 +76,7 @@
     sp<Surface> surface = control->getSurface();
 
     RenderNode* rootNode = new RenderNode();
-    rootNode->incStrong(0);
+    rootNode->incStrong(nullptr);
     rootNode->mutateStagingProperties().setLeftTopRightBottom(0, 0, width, height);
     rootNode->setPropertyFieldsDirty(RenderNode::X | RenderNode::Y);
     rootNode->mutateStagingProperties().setClipToBounds(false);
@@ -123,7 +123,7 @@
 
     sleep(5);
 
-    rootNode->decStrong(0);
+    rootNode->decStrong(nullptr);
 
     printf("Success!\n");
     return 0;