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/LayerCache.cpp b/libs/hwui/LayerCache.cpp
index d6703f2..60d4f4f 100644
--- a/libs/hwui/LayerCache.cpp
+++ b/libs/hwui/LayerCache.cpp
@@ -33,7 +33,7 @@
 
 LayerCache::LayerCache(): mSize(0), mMaxSize(MB(DEFAULT_LAYER_CACHE_SIZE)) {
     char property[PROPERTY_VALUE_MAX];
-    if (property_get(PROPERTY_LAYER_CACHE_SIZE, property, NULL) > 0) {
+    if (property_get(PROPERTY_LAYER_CACHE_SIZE, property, nullptr) > 0) {
         INIT_LOGD("  Setting layer cache size to %sMB", property);
         setMaxSize(MB(atof(property)));
     } else {
@@ -84,7 +84,7 @@
                 layer->getFbo());
         mSize -= layer->getWidth() * layer->getHeight() * 4;
         layer->state = Layer::kState_DeletedFromCache;
-        layer->decStrong(0);
+        layer->decStrong(nullptr);
     }
 }
 
@@ -97,7 +97,7 @@
 }
 
 Layer* LayerCache::get(RenderState& renderState, const uint32_t width, const uint32_t height) {
-    Layer* layer = NULL;
+    Layer* layer = nullptr;
 
     LayerEntry entry(width, height);
     ssize_t index = mCache.indexOf(entry);