Add debug checks to catch crashes with WeakCell::cast().

BUG=

Review URL: https://codereview.chromium.org/1009603003

Cr-Commit-Position: refs/heads/master@{#27314}

src/heap/mark-compact.cc

@@ -2098,6 +2098,7 @@ void MarkCompactCollector::RetainMaps() {
   int length = retained_maps->Length();
   int new_length = 0;
   for (int i = 0; i < length; i += 2) {
+    DCHECK(retained_maps->Get(i)->IsWeakCell());
     WeakCell* cell = WeakCell::cast(retained_maps->Get(i));
     if (cell->cleared()) continue;
     int age = Smi::cast(retained_maps->Get(i + 1))->value();
@@ -2348,6 +2349,7 @@ void MarkCompactCollector::ClearNonLiveReferences() {
     if (!table->IsKey(key)) continue;
     uint32_t value_index = table->EntryToValueIndex(i);
     Object* value = table->get(value_index);
+    DCHECK(key->IsWeakCell());
     if (WeakCell::cast(key)->cleared()) {
       have_code_to_deoptimize_ |=
           DependentCode::cast(value)->MarkCodeForDeoptimization(

src/isolate.cc

@@ -2585,6 +2585,7 @@ void Isolate::CheckDetachedContextsAfterGC() {
   int new_length = 0;
   for (int i = 0; i < length; i += 2) {
     int mark_sweeps = Smi::cast(detached_contexts->get(i))->value();
+    DCHECK(detached_contexts->get(i + 1)->IsWeakCell());
     WeakCell* cell = WeakCell::cast(detached_contexts->get(i + 1));
     if (!cell->cleared()) {
       detached_contexts->set(new_length, Smi::FromInt(mark_sweeps + 1));
@@ -2598,6 +2599,7 @@ void Isolate::CheckDetachedContextsAfterGC() {
            length - new_length, length);
     for (int i = 0; i < new_length; i += 2) {
       int mark_sweeps = Smi::cast(detached_contexts->get(i))->value();
+      DCHECK(detached_contexts->get(i + 1)->IsWeakCell());
       WeakCell* cell = WeakCell::cast(detached_contexts->get(i + 1));
       if (mark_sweeps > 3) {
         PrintF("detached context 0x%p\n survived %d GCs (leak?)\n",

src/objects-inl.h

@@ -2349,6 +2349,7 @@ void FixedDoubleArray::FillWithHoles(int from, int to) {
 Object* WeakFixedArray::Get(int index) const {
   Object* raw = FixedArray::cast(this)->get(index + kFirstIndex);
   if (raw->IsSmi()) return raw;
+  DCHECK(raw->IsWeakCell());
   return WeakCell::cast(raw)->value();
 }
 

src/objects.cc

@@ -10364,6 +10364,7 @@ Handle<Object> Script::GetNameOrSourceURL(Handle<Script> script) {
 Handle<JSObject> Script::GetWrapper(Handle<Script> script) {
   Isolate* isolate = script->GetIsolate();
   if (!script->wrapper()->IsUndefined()) {
+    DCHECK(script->wrapper()->IsWeakCell());
     Handle<WeakCell> cell(WeakCell::cast(script->wrapper()));
     if (!cell->cleared()) {
       // Return a handle for the existing script wrapper from the cache.

src/transitions.h

@@ -68,6 +68,7 @@ class TransitionArray: public FixedArray {
   }
   static inline Map* GetSimpleTransition(Object* raw_transition) {
     DCHECK(IsSimpleTransition(raw_transition));
+    DCHECK(raw_transition->IsWeakCell());
     return Map::cast(WeakCell::cast(raw_transition)->value());
   }
   static inline bool IsFullTransitionArray(Object* raw_transitions) {

src/type-feedback-vector.cc

@@ -435,6 +435,7 @@ int FeedbackNexus::ExtractMaps(MapHandleList* maps) const {
     // [map, handler, map, handler, ... ]
     DCHECK(array->length() >= 2);
     for (int i = 0; i < array->length(); i += 2) {
+      DCHECK(array->get(i)->IsWeakCell());
       WeakCell* cell = WeakCell::cast(array->get(i));
       if (!cell->cleared()) {
         Map* map = Map::cast(cell->value());
@@ -464,6 +465,7 @@ MaybeHandle<Code> FeedbackNexus::FindHandlerForMap(Handle<Map> map) const {
     }
     FixedArray* array = FixedArray::cast(feedback);
     for (int i = 0; i < array->length(); i += 2) {
+      DCHECK(array->get(i)->IsWeakCell());
       WeakCell* cell = WeakCell::cast(array->get(i));
       if (!cell->cleared()) {
         Map* array_map = Map::cast(cell->value());
@@ -502,6 +504,7 @@ bool FeedbackNexus::FindHandlers(CodeHandleList* code_list, int length) const {
     // Be sure to skip handlers whose maps have been cleared.
     DCHECK(array->length() >= 2);
     for (int i = 0; i < array->length(); i += 2) {
+      DCHECK(array->get(i)->IsWeakCell());
       WeakCell* cell = WeakCell::cast(array->get(i));
       if (!cell->cleared()) {
         Code* code = Code::cast(array->get(i + 1));