Reapply r10158: Distinguish weak references in heap snapshots, group GC roots.

src/profile-generator.h

Index: src/profile-generator.h
diff --git a/src/profile-generator.h b/src/profile-generator.h
index 44be3db78c9b3938a54215b83b6b936b724d7429..b47ce8255a844dcfed2bd0bed182ba155b5b0cd0 100644
--- a/src/profile-generator.h
+++ b/src/profile-generator.h
@@ -455,7 +455,8 @@ class HeapGraphEdge BASE_EMBEDDED {
     kProperty = v8::HeapGraphEdge::kProperty,
     kInternal = v8::HeapGraphEdge::kInternal,
     kHidden = v8::HeapGraphEdge::kHidden,
-    kShortcut = v8::HeapGraphEdge::kShortcut
+    kShortcut = v8::HeapGraphEdge::kShortcut,
+    kWeak = v8::HeapGraphEdge::kWeak
   };
 
   HeapGraphEdge() { }
@@ -465,7 +466,7 @@ class HeapGraphEdge BASE_EMBEDDED {
 
   Type type() { return static_cast<Type>(type_); }
   int index() {
-    ASSERT(type_ == kElement || type_ == kHidden);
+    ASSERT(type_ == kElement || type_ == kHidden || type_ == kWeak);
     return index_;
   }
   const char* name() {
@@ -588,7 +589,8 @@ class HeapEntry BASE_EMBEDDED {
   int EntrySize() { return EntriesSize(1, children_count_, retainers_count_); }
   int RetainedSize(bool exact);
 
-  void Print(int max_depth, int indent);
+  void Print(
+      const char* prefix, const char* edge_name, int max_depth, int indent);
 
   Handle<HeapObject> GetHeapObject();
 
@@ -661,6 +663,7 @@ class HeapSnapshot {
   HeapEntry* root() { return root_entry_; }
   HeapEntry* gc_roots() { return gc_roots_entry_; }
   HeapEntry* natives_root() { return natives_root_entry_; }
+  HeapEntry* gc_subroot(int index) { return gc_subroot_entries_[index]; }
   List<HeapEntry*>* entries() { return &entries_; }
   int raw_entries_size() { return raw_entries_size_; }
 
@@ -674,6 +677,9 @@ class HeapSnapshot {
                       int retainers_count);
   HeapEntry* AddRootEntry(int children_count);
   HeapEntry* AddGcRootsEntry(int children_count, int retainers_count);
+  HeapEntry* AddGcSubrootEntry(int tag,
+                               int children_count,
+                               int retainers_count);
   HeapEntry* AddNativesRootEntry(int children_count, int retainers_count);
   void ClearPaint();
   HeapEntry* GetEntryById(uint64_t id);
@@ -695,6 +701,7 @@ class HeapSnapshot {
   HeapEntry* root_entry_;
   HeapEntry* gc_roots_entry_;
   HeapEntry* natives_root_entry_;
+  HeapEntry* gc_subroot_entries_[VisitorSynchronization::kNumberOfSyncTags];
   char* raw_entries_;
   List<HeapEntry*> entries_;
   bool entries_sorted_;
@@ -716,10 +723,13 @@ class HeapObjectsMap {
   void MoveObject(Address from, Address to);
 
   static uint64_t GenerateId(v8::RetainedObjectInfo* info);
+  static inline uint64_t GetNthGcSubrootId(int delta);
 
+  static const int kObjectIdStep = 2;
   static const uint64_t kInternalRootObjectId;
   static const uint64_t kGcRootsObjectId;
   static const uint64_t kNativesRootObjectId;
+  static const uint64_t kGcRootsFirstSubrootId;
   static const uint64_t kFirstAvailableObjectId;
 
  private:
@@ -969,6 +979,11 @@ class V8HeapExplorer : public HeapEntriesAllocator {
                           HeapEntry* parent,
                           int index,
                           Object* child);
+  void SetWeakReference(HeapObject* parent_obj,
+                        HeapEntry* parent_entry,
+                        int index,
+                        Object* child_obj,
+                        int field_offset);
   void SetPropertyReference(HeapObject* parent_obj,
                             HeapEntry* parent,
                             String* reference_name,
@@ -981,11 +996,16 @@ class V8HeapExplorer : public HeapEntriesAllocator {
                                     Object* child);
   void SetRootShortcutReference(Object* child);
   void SetRootGcRootsReference();
-  void SetGcRootsReference(Object* child);
+  void SetGcRootsReference(VisitorSynchronization::SyncTag tag);
+  void SetGcSubrootReference(
+      VisitorSynchronization::SyncTag tag, bool is_weak, Object* child);
   void TagObject(Object* obj, const char* tag);
 
   HeapEntry* GetEntry(Object* obj);
 
+  static inline HeapObject* GetNthGcSubrootObject(int delta);
+  static inline int GetGcSubrootOrder(HeapObject* subroot);
+
   Heap* heap_;
   HeapSnapshot* snapshot_;
   HeapSnapshotsCollection* collection_;
@@ -994,8 +1014,11 @@ class V8HeapExplorer : public HeapEntriesAllocator {
   HeapObjectsSet objects_tags_;
 
   static HeapObject* const kGcRootsObject;
+  static HeapObject* const kFirstGcSubrootObject;
+  static HeapObject* const kLastGcSubrootObject;
 
   friend class IndexedReferencesExtractor;
+  friend class GcSubrootsEnumerator;
   friend class RootsReferencesExtractor;
 
   DISALLOW_COPY_AND_ASSIGN(V8HeapExplorer);