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/FboCache.cpp b/libs/hwui/FboCache.cpp
index beef7be..b54d532 100644
--- a/libs/hwui/FboCache.cpp
+++ b/libs/hwui/FboCache.cpp
@@ -31,7 +31,7 @@
 
 FboCache::FboCache(): mMaxSize(DEFAULT_FBO_CACHE_SIZE) {
     char property[PROPERTY_VALUE_MAX];
-    if (property_get(PROPERTY_FBO_CACHE_SIZE, property, NULL) > 0) {
+    if (property_get(PROPERTY_FBO_CACHE_SIZE, property, nullptr) > 0) {
         INIT_LOGD("  Setting fbo cache size to %s", property);
         mMaxSize = atoi(property);
     } else {