[objects] Clarify 32-bit offsets in 64-bit fields

These fields relied on the assumption that 64-bit big-endian
architectures had sizeof(int) == 4. Any architecture violating this
assumption would result in an OOB access.

Bug: 
Change-Id: I682ecb6a2da2cf84e8b24f1c1e608d7fc23f5bdc
Reviewed-on: https://chromium-review.googlesource.com/793431Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49673}

src/objects/js-array.h

@@ -225,7 +225,7 @@ class JSArrayBuffer : public JSObject {
 #if V8_TARGET_LITTLE_ENDIAN || !V8_HOST_ARCH_64_BIT
   static const int kBitFieldOffset = kBitFieldSlot;
 #else
-  static const int kBitFieldOffset = kBitFieldSlot + kIntSize;
+  static const int kBitFieldOffset = kBitFieldSlot + kInt32Size;
 #endif
   static const int kSize = kBitFieldSlot + kPointerSize;
 

src/objects/name-inl.h

@@ -41,7 +41,7 @@ void Name::set_hash_field(uint32_t value) {
   WRITE_UINT32_FIELD(this, kHashFieldOffset, value);
 #if V8_HOST_ARCH_64_BIT
 #if V8_TARGET_LITTLE_ENDIAN
-  WRITE_UINT32_FIELD(this, kHashFieldSlot + kIntSize, 0);
+  WRITE_UINT32_FIELD(this, kHashFieldSlot + kInt32Size, 0);
 #else
   WRITE_UINT32_FIELD(this, kHashFieldSlot, 0);
 #endif

src/objects/name.h

@@ -65,7 +65,7 @@ class Name : public HeapObject {
 #if V8_TARGET_LITTLE_ENDIAN || !V8_HOST_ARCH_64_BIT
   static const int kHashFieldOffset = kHashFieldSlot;
 #else
-  static const int kHashFieldOffset = kHashFieldSlot + kIntSize;
+  static const int kHashFieldOffset = kHashFieldSlot + kInt32Size;
 #endif
   static const int kSize = kHashFieldSlot + kPointerSize;