Remove conservative sweeping.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index ef947c95f780bcbd5a552f0c84565ae3b2a06236..0d91b23e90a1bea335ee918f447f72e5538c10b0 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -713,14 +713,11 @@ class Heap {
       const GCCallbackFlags gc_callback_flags = kNoGCCallbackFlags);
 
   static const int kNoGCFlags = 0;
-  static const int kSweepPreciselyMask = 1;
-  static const int kReduceMemoryFootprintMask = 2;
-  static const int kAbortIncrementalMarkingMask = 4;
-
-  // Making the heap iterable requires us to sweep precisely and abort any
-  // incremental marking as well.
-  static const int kMakeHeapIterableMask =
-      kSweepPreciselyMask | kAbortIncrementalMarkingMask;
+  static const int kReduceMemoryFootprintMask = 1;
+  static const int kAbortIncrementalMarkingMask = 2;
+
+  // Making the heap iterable requires us to abort incremental marking.
+  static const int kMakeHeapIterableMask = kAbortIncrementalMarkingMask;
 
   // Performs a full garbage collection.  If (flags & kMakeHeapIterableMask) is
   // non-zero, then the slower precise sweeper is used, which leaves the heap