Replace NULL with nullptr

Also fixed some lines that were too long, and a few other minor
details.

Change-Id: I6efba5fb6e03eb5d0a300fddb2a75bf8e2f175cb
diff --git a/runtime/gc/space/dlmalloc_space.cc b/runtime/gc/space/dlmalloc_space.cc
index 225861d..7b1a421 100644
--- a/runtime/gc/space/dlmalloc_space.cc
+++ b/runtime/gc/space/dlmalloc_space.cc
@@ -39,7 +39,7 @@
     : MallocSpace(name, mem_map, begin, end, limit, growth_limit, true, can_move_objects,
                   starting_size, initial_size),
       mspace_(mspace) {
-  CHECK(mspace != NULL);
+  CHECK(mspace != nullptr);
 }
 
 DlMallocSpace* DlMallocSpace::CreateFromMemMap(MemMap* mem_map, const std::string& name,
@@ -176,7 +176,7 @@
 }
 
 size_t DlMallocSpace::FreeList(Thread* self, size_t num_ptrs, mirror::Object** ptrs) {
-  DCHECK(ptrs != NULL);
+  DCHECK(ptrs != nullptr);
 
   // Don't need the lock to calculate the size of the freed pointers.
   size_t bytes_freed = 0;
@@ -232,7 +232,7 @@
                       void* arg) {
   MutexLock mu(Thread::Current(), lock_);
   mspace_inspect_all(mspace_, callback, arg);
-  callback(NULL, NULL, 0, arg);  // Indicate end of a space.
+  callback(nullptr, nullptr, 0, arg);  // Indicate end of a space.
 }
 
 size_t DlMallocSpace::GetFootprint() {