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/renderthread/RenderTask.h b/libs/hwui/renderthread/RenderTask.h
index 1554a16..89c3a7d 100644
--- a/libs/hwui/renderthread/RenderTask.h
+++ b/libs/hwui/renderthread/RenderTask.h
@@ -47,7 +47,7 @@
 
 class ANDROID_API RenderTask {
 public:
-    ANDROID_API RenderTask() : mNext(0), mRunAt(0) {}
+    ANDROID_API RenderTask() : mNext(nullptr), mRunAt(0) {}
     ANDROID_API virtual ~RenderTask() {}
 
     ANDROID_API virtual void run() = 0;
@@ -61,7 +61,7 @@
     // Takes ownership of task, caller owns lock and signal
     SignalingRenderTask(RenderTask* task, Mutex* lock, Condition* signal)
             : mTask(task), mLock(lock), mSignal(signal) {}
-    virtual void run();
+    virtual void run() override;
 
 private:
     RenderTask* mTask;
@@ -74,12 +74,12 @@
 class MethodInvokeRenderTask : public RenderTask {
 public:
     MethodInvokeRenderTask(RunnableMethod method)
-        : mMethod(method), mReturnPtr(0) {}
+        : mMethod(method), mReturnPtr(nullptr) {}
 
     void* payload() { return mData; }
     void setReturnPtr(void** retptr) { mReturnPtr = retptr; }
 
-    virtual void run() {
+    virtual void run() override {
         void* retval = mMethod(mData);
         if (mReturnPtr) {
             *mReturnPtr = retval;