[in-place weak refs] Mark suitable MaybeObject funcs const

BUG=v8:7308

Change-Id: Id05fe2480d7cda8038740aaae949cc707686171f
Reviewed-on: https://chromium-review.googlesource.com/1174439Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55123}

src/globals.h

@@ -1528,7 +1528,7 @@ V8_INLINE static bool HasWeakHeapObjectTag(const Object* value) {
           kWeakHeapObjectTag);
 }
 
-V8_INLINE static bool IsClearedWeakHeapObject(MaybeObject* value) {
+V8_INLINE static bool IsClearedWeakHeapObject(const MaybeObject* value) {
   return reinterpret_cast<intptr_t>(value) == kClearedWeakHeapObject;
 }
 

src/objects/maybe-object-inl.h

@@ -24,7 +24,7 @@ Smi* MaybeObject::ToSmi() {
   return Smi::cast(reinterpret_cast<Object*>(this));
 }
 
-bool MaybeObject::IsStrongOrWeakHeapObject() {
+bool MaybeObject::IsStrongOrWeakHeapObject() const {
   if (IsSmi() || IsClearedWeakHeapObject()) {
     return false;
   }
@@ -51,7 +51,7 @@ bool MaybeObject::ToStrongOrWeakHeapObject(
   return true;
 }
 
-bool MaybeObject::IsStrongHeapObject() {
+bool MaybeObject::IsStrongHeapObject() const {
   return !HasWeakHeapObjectTag(this) && !IsSmi();
 }
 
@@ -68,11 +68,11 @@ HeapObject* MaybeObject::ToStrongHeapObject() {
   return reinterpret_cast<HeapObject*>(this);
 }
 
-bool MaybeObject::IsWeakHeapObject() {
+bool MaybeObject::IsWeakHeapObject() const {
   return HasWeakHeapObjectTag(this) && !IsClearedWeakHeapObject();
 }
 
-bool MaybeObject::IsWeakOrClearedHeapObject() {
+bool MaybeObject::IsWeakOrClearedHeapObject() const {
   return HasWeakHeapObjectTag(this);
 }
 
@@ -102,7 +102,7 @@ Object* MaybeObject::GetHeapObjectOrSmi() {
   return GetHeapObject();
 }
 
-bool MaybeObject::IsObject() { return IsSmi() || IsStrongHeapObject(); }
+bool MaybeObject::IsObject() const { return IsSmi() || IsStrongHeapObject(); }
 
 Object* MaybeObject::ToObject() {
   DCHECK(!HasWeakHeapObjectTag(this));

src/objects/maybe-object.h

@@ -25,19 +25,19 @@ class MaybeObject {
   inline bool ToSmi(Smi** value);
   inline Smi* ToSmi();
 
-  bool IsClearedWeakHeapObject() {
+  bool IsClearedWeakHeapObject() const {
     return ::v8::internal::IsClearedWeakHeapObject(this);
   }
 
-  inline bool IsStrongOrWeakHeapObject();
+  inline bool IsStrongOrWeakHeapObject() const;
   inline bool ToStrongOrWeakHeapObject(HeapObject** result);
   inline bool ToStrongOrWeakHeapObject(HeapObject** result,
                                        HeapObjectReferenceType* reference_type);
-  inline bool IsStrongHeapObject();
+  inline bool IsStrongHeapObject() const;
   inline bool ToStrongHeapObject(HeapObject** result);
   inline HeapObject* ToStrongHeapObject();
-  inline bool IsWeakHeapObject();
-  inline bool IsWeakOrClearedHeapObject();
+  inline bool IsWeakHeapObject() const;
+  inline bool IsWeakOrClearedHeapObject() const;
   inline bool ToWeakHeapObject(HeapObject** result);
   inline HeapObject* ToWeakHeapObject();
 
@@ -45,7 +45,7 @@ class MaybeObject {
   inline HeapObject* GetHeapObject();
   inline Object* GetHeapObjectOrSmi();
 
-  inline bool IsObject();
+  inline bool IsObject() const;
   inline Object* ToObject();
 
   static MaybeObject* FromSmi(Smi* smi) {