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/utils/Timing.h b/libs/hwui/utils/Timing.h
index eced987..dd8847a 100644
--- a/libs/hwui/utils/Timing.h
+++ b/libs/hwui/utils/Timing.h
@@ -24,12 +24,12 @@
 public:
     MethodTimer(const char* name)
             : mMethodName(name) {
-        gettimeofday(&mStart, NULL);
+        gettimeofday(&mStart, nullptr);
     }
 
     ~MethodTimer() {
         struct timeval stop;
-        gettimeofday(&stop, NULL);
+        gettimeofday(&stop, nullptr);
         long long elapsed = (stop.tv_sec * 1000000) - (mStart.tv_sec * 1000000)
                 + (stop.tv_usec - mStart.tv_usec);
         ALOGD("%s took %.2fms", mMethodName, elapsed / 1000.0);