Update V8 to r6768 as required by WebKit r78450

Change-Id: Ib8868ff7147a76547a8d1d85f257ebe8546a3d3f
diff --git a/src/heap-profiler.cc b/src/heap-profiler.cc
index dfda7c6..732d2f4 100644
--- a/src/heap-profiler.cc
+++ b/src/heap-profiler.cc
@@ -373,6 +373,7 @@
   bool generation_completed = true;
   switch (s_type) {
     case HeapSnapshot::kFull: {
+      Heap::CollectAllGarbage(true);
       HeapSnapshotGenerator generator(result, control);
       generation_completed = generator.GenerateSnapshot();
       break;
@@ -808,7 +809,7 @@
 
 
 void AggregatedHeapSnapshotGenerator::GenerateSnapshot() {
-  HeapIterator iterator(HeapIterator::kFilterFreeListNodes);
+  HeapIterator iterator(HeapIterator::kFilterUnreachable);
   for (HeapObject* obj = iterator.next(); obj != NULL; obj = iterator.next()) {
     CollectStats(obj);
     agg_snapshot_->js_cons_profile()->CollectStats(obj);