Reland "Allocation site support for monomorphic StringAdds in BinaryOps".

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index b295bae9fc97b527f57bcb57b4e0d6f237a7570c..cf21e802ebc14b32afd64beb0a891939bc213ea5 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -10477,6 +10477,12 @@ Object* Code::FindNthObject(int n, Map* match_map) {
 }
 
 
+AllocationSite* Code::FindFirstAllocationSite() {
+  Object* result = FindNthObject(1, GetHeap()->allocation_site_map());
+  return (result != NULL) ? AllocationSite::cast(result) : NULL;
+}
+
+
 Map* Code::FindFirstMap() {
   Object* result = FindNthObject(1, GetHeap()->meta_map());
   return (result != NULL) ? Map::cast(result) : NULL;