Add ObjectMoveEvent reporting for the Heap Profiler into MarkCompact.

src/profile-generator.cc

Index: src/profile-generator.cc
diff --git a/src/profile-generator.cc b/src/profile-generator.cc
index 814e9b3e9d578a62850a3dab5d46d41bdd022bf2..6bd8b46d58fc06a9187beb9fcb16c4f3edef5240 100644
--- a/src/profile-generator.cc
+++ b/src/profile-generator.cc
@@ -1398,10 +1398,12 @@ void HeapObjectsMap::MoveObject(Address from, Address to) {
   if (entry != NULL) {
     void* value = entry->value;
     entries_map_.Remove(from, AddressHash(from));
-    entry = entries_map_.Lookup(to, AddressHash(to), true);
-    // We can have an entry at the new location, it is OK, as GC can overwrite
-    // dead objects with alive objects being moved.
-    entry->value = value;
+    if (to != NULL) {
+      entry = entries_map_.Lookup(to, AddressHash(to), true);
+      // We can have an entry at the new location, it is OK, as GC can overwrite
+      // dead objects with alive objects being moved.
+      entry->value = value;
+    }
   }
 }