Using override keyword in ObjectVisitor class hierarchy.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index af88abc0e9eb6da777574d455f6cbc0cc8a58890..5d50d181d218ac01007e0efdb8bdf309facce736 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -1091,7 +1091,7 @@ void Heap::MoveElements(FixedArray* array, int dst_index, int src_index,
 // Helper class for verifying the string table.
 class StringTableVerifier : public ObjectVisitor {
  public:
-  void VisitPointers(Object** start, Object** end) {
+  void VisitPointers(Object** start, Object** end) override {
     // Visit all HeapObject pointers in [start, end).
     for (Object** p = start; p < end; p++) {
       if ((*p)->IsHeapObject()) {
@@ -1451,7 +1451,8 @@ void Heap::MarkCompactPrologue() {
 class VerifyNonPointerSpacePointersVisitor : public ObjectVisitor {
  public:
   explicit VerifyNonPointerSpacePointersVisitor(Heap* heap) : heap_(heap) {}
-  void VisitPointers(Object** start, Object** end) {
+
+  void VisitPointers(Object** start, Object** end) override {
     for (Object** current = start; current < end; current++) {
       if ((*current)->IsHeapObject()) {
         CHECK(!heap_->InNewSpace(HeapObject::cast(*current)));
@@ -5398,7 +5399,7 @@ void Heap::FatalProcessOutOfMemory(const char* location, bool take_snapshot) {
 
 class PrintHandleVisitor : public ObjectVisitor {
  public:
-  void VisitPointers(Object** start, Object** end) {
+  void VisitPointers(Object** start, Object** end) override {
     for (Object** p = start; p < end; p++)
       PrintF("  handle %p to %p\n", reinterpret_cast<void*>(p),
              reinterpret_cast<void*>(*p));
@@ -5417,10 +5418,10 @@ void Heap::PrintHandles() {
 class CheckHandleCountVisitor : public ObjectVisitor {
  public:
   CheckHandleCountVisitor() : handle_count_(0) {}
-  ~CheckHandleCountVisitor() {
+  ~CheckHandleCountVisitor() override {
     CHECK(handle_count_ < HandleScope::kCheckHandleThreshold);
   }
-  void VisitPointers(Object** start, Object** end) {
+  void VisitPointers(Object** start, Object** end) override {
     handle_count_ += end - start;
   }
 
@@ -5567,7 +5568,7 @@ class UnreachableObjectsFilter : public HeapObjectsFilter {
    public:
     MarkingVisitor() : marking_stack_(10) {}
 
-    void VisitPointers(Object** start, Object** end) {
+    void VisitPointers(Object** start, Object** end) override {
       for (Object** p = start; p < end; p++) {
         if (!(*p)->IsHeapObject()) continue;
         HeapObject* obj = HeapObject::cast(*p);
@@ -5676,7 +5677,8 @@ Object* const PathTracer::kAnyGlobalObject = NULL;
 class PathTracer::MarkVisitor : public ObjectVisitor {
  public:
   explicit MarkVisitor(PathTracer* tracer) : tracer_(tracer) {}
-  void VisitPointers(Object** start, Object** end) {
+
+  void VisitPointers(Object** start, Object** end) override {
     // Scan all HeapObject pointers in [start, end)
     for (Object** p = start; !tracer_->found() && (p < end); p++) {
       if ((*p)->IsHeapObject()) tracer_->MarkRecursively(p, this);
@@ -5691,7 +5693,8 @@ class PathTracer::MarkVisitor : public ObjectVisitor {
 class PathTracer::UnmarkVisitor : public ObjectVisitor {
  public:
   explicit UnmarkVisitor(PathTracer* tracer) : tracer_(tracer) {}
-  void VisitPointers(Object** start, Object** end) {
+
+  void VisitPointers(Object** start, Object** end) override {
     // Scan all HeapObject pointers in [start, end)
     for (Object** p = start; p < end; p++) {
       if ((*p)->IsHeapObject()) tracer_->UnmarkRecursively(p, this);