This value is required for showing the heap snapshot delta in Summary view of DevTools.Profiler.

At the moment it is evaluating on the front-end side and this is cost us 2 * (load time + parse time + traverse via snapshot) because I need this value for two previous snapshots.

BUG=none
TEST=test-heap-profiler

Review URL: https://chromiumcodereview.appspot.com/9858016

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11150 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8-profiler.h

@@ -347,6 +347,9 @@ class V8EXPORT HeapSnapshot {
   /** Returns a node by index. */
   const HeapGraphNode* GetNode(int index) const;
 
+  /** Returns a max seen JS object Id. */
+  SnapshotObjectId GetMaxSnapshotJSObjectId() const;
+
   /**
    * Deletes the snapshot and removes it from HeapProfiler's list.
    * All pointers to nodes, edges and paths previously returned become

src/api.cc

@@ -6157,6 +6157,13 @@ const HeapGraphNode* HeapSnapshot::GetNode(int index) const {
 }
 
 
+SnapshotObjectId HeapSnapshot::GetMaxSnapshotJSObjectId() const {
+  i::Isolate* isolate = i::Isolate::Current();
+  IsDeadCheck(isolate, "v8::HeapSnapshot::GetMaxSnapshotJSObjectId");
+  return ToInternal(this)->max_snapshot_js_object_id();
+}
+
+
 void HeapSnapshot::Serialize(OutputStream* stream,
                              HeapSnapshot::SerializationFormat format) const {
   i::Isolate* isolate = i::Isolate::Current();

src/profile-generator.cc

@@ -1133,7 +1133,8 @@ HeapSnapshot::HeapSnapshot(HeapSnapshotsCollection* collection,
       gc_roots_entry_(NULL),
       natives_root_entry_(NULL),
       raw_entries_(NULL),
-      entries_sorted_(false) {
+      entries_sorted_(false),
+      max_snapshot_js_object_id_(0) {
   STATIC_CHECK(
       sizeof(HeapGraphEdge) ==
       SnapshotSizeConstants<kPointerSize>::kExpectedHeapGraphEdgeSize);
@@ -1223,6 +1224,11 @@ HeapEntry* HeapSnapshot::AddEntry(HeapEntry::Type type,
                                   int retainers_count) {
   HeapEntry* entry = GetNextEntryToInit();
   entry->Init(this, type, name, id, size, children_count, retainers_count);
+
+  // Track only js objects. They have odd ids.
+  if (id % HeapObjectsMap::kObjectIdStep && id > max_snapshot_js_object_id_)
+    max_snapshot_js_object_id_ = id;
+
   return entry;
 }
 

src/profile-generator.h

@@ -35,8 +35,6 @@
 namespace v8 {
 namespace internal {
 
-typedef uint32_t SnapshotObjectId;
-
 class TokenEnumerator {
  public:
   TokenEnumerator();
@@ -647,6 +645,9 @@ class HeapSnapshot {
   HeapEntry* gc_subroot(int index) { return gc_subroot_entries_[index]; }
   List<HeapEntry*>* entries() { return &entries_; }
   size_t raw_entries_size() { return raw_entries_size_; }
+  SnapshotObjectId max_snapshot_js_object_id() const {
+    return max_snapshot_js_object_id_;
+  }
 
   void AllocateEntries(
       int entries_count, int children_count, int retainers_count);
@@ -687,6 +688,7 @@ class HeapSnapshot {
   List<HeapEntry*> entries_;
   bool entries_sorted_;
   size_t raw_entries_size_;
+  SnapshotObjectId max_snapshot_js_object_id_;
 
   friend class HeapSnapshotTester;
 

test/cctest/test-heap-profiler.cc

@@ -422,6 +422,11 @@ TEST(HeapEntryIdsAndGC) {
   const v8::HeapSnapshot* snapshot2 =
       v8::HeapProfiler::TakeSnapshot(v8_str("s2"));
 
+  // Second snapshot has one more string, it is it's name 's2'.
+  CHECK_EQ_SNAPSHOT_OBJECT_ID(
+    snapshot1->GetMaxSnapshotJSObjectId() + i::HeapObjectsMap::kObjectIdStep,
+    snapshot2->GetMaxSnapshotJSObjectId());
+
   const v8::HeapGraphNode* global1 = GetGlobalObject(snapshot1);
   const v8::HeapGraphNode* global2 = GetGlobalObject(snapshot2);
   CHECK_NE_SNAPSHOT_OBJECT_ID(0, global1->GetId());