Reland of "Enable inobject double fields unboxing for 64-bit archs."

src/heap/store-buffer.cc

Index: src/heap/store-buffer.cc
diff --git a/src/heap/store-buffer.cc b/src/heap/store-buffer.cc
index 4b94a95761774a05d3b44affed0b510caec4bbcd..5fd4ce34f3aee6913c42fe3c292b1dea5f0ea8ab 100644
--- a/src/heap/store-buffer.cc
+++ b/src/heap/store-buffer.cc
@@ -519,7 +519,7 @@ void StoreBuffer::IteratePointersToNewSpace(ObjectSlotCallback slot_callback,
                 if (!has_only_tagged_fields) {
                   for (Address slot = start_address; slot < end_address;
                        slot += kPointerSize) {
-                    if (helper.IsTagged(slot - obj_address)) {
+                    if (helper.IsTagged(static_cast<int>(slot - obj_address))) {
                       // TODO(ishell): call this once for contiguous region
                       // of tagged fields.
                       FindPointersToNewSpaceInRegion(slot, slot + kPointerSize,