Basic array capacity feedback via allocation sites.

src/builtins.cc

Index: src/builtins.cc
diff --git a/src/builtins.cc b/src/builtins.cc
index c52d22852d0deb8fd4f3e9a0ea9462eadbab6147..40483c2dc9a9463c3328b8038e3119a2234bb6e3 100644
--- a/src/builtins.cc
+++ b/src/builtins.cc
@@ -348,6 +348,14 @@ BUILTIN(ArrayPush) {
           ElementsAccessor::kCopyToEndAndInitializeToHole);
 
       elms = new_elms;
+
+      // Do we have an AllocationMemento, to store this feedback?
+      AllocationMemento* memento =
+          isolate->heap()->FindAllocationMemento(*array);
+      if (memento != NULL && memento->IsValid()) {
+        AllocationSite* site = memento->GetAllocationSite();
+        site->DigestInitialElementsCapacityFeedback(new_length);
+      }
     }
 
     // Add the provided values.