Show names for the strong roots in heap snapshot.

src/profile-generator.cc

Index: src/profile-generator.cc
diff --git a/src/profile-generator.cc b/src/profile-generator.cc
index 5d74c42ac1e0a6ec1310734bd5816a7203da29b6..ddc42f9763b774050c7d0e89f0118d96e0a1e282 100644
--- a/src/profile-generator.cc
+++ b/src/profile-generator.cc
@@ -1736,7 +1736,8 @@ V8HeapExplorer::V8HeapExplorer(
       snapshot_(snapshot),
       collection_(snapshot_->collection()),
       progress_(progress),
-      filler_(NULL) {
+      filler_(NULL),
+      gc_subroot_names_(HeapEntriesMap::HeapThingsMatch) {
 }
 
 
@@ -2653,11 +2654,49 @@ void V8HeapExplorer::SetGcSubrootReference(
     VisitorSynchronization::SyncTag tag, bool is_weak, Object* child_obj) {
   HeapEntry* child_entry = GetEntry(child_obj);
   if (child_entry != NULL) {
-    filler_->SetIndexedAutoIndexReference(
-        is_weak ? HeapGraphEdge::kWeak : HeapGraphEdge::kElement,
-        GetNthGcSubrootObject(tag), snapshot_->gc_subroot(tag),
-        child_obj, child_entry);
-  }
+    const char* name = GetGcSubrootName(child_obj);
+    if (name != NULL) {
+      filler_->SetNamedReference(
+          HeapGraphEdge::kInternal,
+          GetNthGcSubrootObject(tag), snapshot_->gc_subroot(tag),
+          name,
+          child_obj, child_entry);
+    } else {
+      filler_->SetIndexedAutoIndexReference(
+          is_weak ? HeapGraphEdge::kWeak : HeapGraphEdge::kElement,
+          GetNthGcSubrootObject(tag), snapshot_->gc_subroot(tag),
+          child_obj, child_entry);
+    }
+  }
+}
+
+
+const char* V8HeapExplorer::GetGcSubrootName(Object* object) {
+  if (gc_subroot_names_.occupancy() == 0) {
+    HashMap::Entry* entry;
+    Object* obj;
+#define NAME_ENTRY(name) \
+    obj = heap_->name(); \
+    if (obj != NULL) { \
+      entry = gc_subroot_names_.Lookup(obj, HeapEntriesMap::Hash(obj), true); \
+      entry->value = const_cast<char*>(#name); \
+    }
+#define ROOT_NAME(type, name, camel_name) NAME_ENTRY(name)
+    STRONG_ROOT_LIST(ROOT_NAME)
+#undef ROOT_NAME
+#define STRUCT_MAP_NAME(NAME, Name, name) NAME_ENTRY(name##_map)
+    STRUCT_LIST(STRUCT_MAP_NAME)
+#undef STRUCT_MAP_NAME
+#define SYMBOL_NAME(name, str) NAME_ENTRY(name)
+    SYMBOL_LIST(SYMBOL_NAME)
+#undef SYMBOL_NAME
+#undef NAME_ENTRY
+    CHECK(gc_subroot_names_.occupancy() > 0);
+    CHECK(gc_subroot_names_.occupancy() <= Heap::kStrongRootListLength);
+  }
+  HashMap::Entry* entry = gc_subroot_names_.Lookup(
+      object, HeapEntriesMap::Hash(object), false);
+  return entry != NULL ? reinterpret_cast<const char*>(entry->value) : NULL;
 }