Revert of Enable inobject double fields unboxing for 64-bit archs. (patchset...

Revert of Enable inobject double fields unboxing for 64-bit archs. (patchset #3 id:40001 of https://codereview.chromium.org/753503002/)

Reason for revert:
GCMole and gc-stress issues.

Original issue's description:
> Enable inobject double fields unboxing for 64-bit archs.

TBR=verwaest@chromium.org
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/751863002

Cr-Commit-Position: refs/heads/master@{#25470}

src/globals.h

@@ -84,7 +84,7 @@ namespace internal {
 
 // Determine whether double field unboxing feature is enabled.
 #if (V8_TARGET_ARCH_X64 || V8_TARGET_ARCH_ARM64)
-#define V8_DOUBLE_FIELDS_UNBOXING 1
+#define V8_DOUBLE_FIELDS_UNBOXING 0
 #else
 #define V8_DOUBLE_FIELDS_UNBOXING 0
 #endif

src/heap/mark-compact.cc

@@ -2764,8 +2764,7 @@ void MarkCompactCollector::MigrateObject(HeapObject* dst, HeapObject* src,
 
 #if V8_DOUBLE_FIELDS_UNBOXING
       if (!may_contain_raw_values &&
-          (has_only_tagged_fields ||
-           helper.IsTagged(static_cast<int>(src_slot - src_addr))))
+          (has_only_tagged_fields || helper.IsTagged(src_slot - src_addr)))
 #else
       if (!may_contain_raw_values)
 #endif

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(static_cast<int>(slot - obj_address))) {
+                    if (helper.IsTagged(slot - obj_address)) {
                       // TODO(ishell): call this once for contiguous region
                       // of tagged fields.
                       FindPointersToNewSpaceInRegion(slot, slot + kPointerSize,

test/cctest/test-unboxed-doubles.cc

@@ -37,7 +37,7 @@ enum PropertyKind {
   PROP_SMI,
   PROP_DOUBLE,
   PROP_TAGGED,
-  PROP_KIND_NUMBER
+  PROP_KIND_NUMBER,
 };
 
 static Representation representations[PROP_KIND_NUMBER] = {