Simplify allocation tracker API

src/heap-snapshot-generator.cc

Index: src/heap-snapshot-generator.cc
diff --git a/src/heap-snapshot-generator.cc b/src/heap-snapshot-generator.cc
index b77414b32f7286e93a034b279d6eba009b8d466e..271f95c5ca0a40c871a99e822f793d1f078d077e 100644
--- a/src/heap-snapshot-generator.cc
+++ b/src/heap-snapshot-generator.cc
@@ -752,9 +752,10 @@ HeapSnapshotsCollection::~HeapSnapshotsCollection() {
 }
 
 
-void HeapSnapshotsCollection::StartHeapObjectsTracking() {
+void HeapSnapshotsCollection::StartHeapObjectsTracking(bool track_allocations) {
   ids_.UpdateHeapObjectsMap();
-  if (allocation_tracker_ == NULL) {
+  ASSERT(allocation_tracker_ == NULL);
+  if (track_allocations) {
     allocation_tracker_ = new AllocationTracker(&ids_, names());
   }
 }