Revert of [heap] Do not invoke GC to make heap iterable.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 51e4ba1cd5ab84f2fe21d7a424eace49d6ab2f1c..fd788cdbe991c413d00e7ee2ce74ca9b4a7a2371 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -539,6 +539,9 @@
   static const int kAbortIncrementalMarkingMask = 2;
   static const int kFinalizeIncrementalMarkingMask = 4;
 
+  // Making the heap iterable requires us to abort incremental marking.
+  static const int kMakeHeapIterableMask = kAbortIncrementalMarkingMask;
+
   // The roots that have an index less than this are always in old space.
   static const int kOldSpaceRoots = 0x20;
 
@@ -658,6 +661,9 @@
 
   // Converts the given boolean condition to JavaScript boolean value.
   inline Oddball* ToBoolean(bool condition);
+
+  // Check whether the heap is currently iterable.
+  bool IsHeapIterable();
 
   // Notify the heap that a context has been disposed.
   int NotifyContextDisposed(bool dependant_context);
@@ -1024,7 +1030,9 @@
       AllocationSpace space, const char* gc_reason = NULL,
       const GCCallbackFlags gc_callback_flags = kNoGCCallbackFlags);
 
-  // Performs a full garbage collection.
+  // Performs a full garbage collection.  If (flags & kMakeHeapIterableMask) is
+  // non-zero, then the slower precise sweeper is used, which leaves the heap
+  // in a state where we can iterate over the heap visiting all objects.
   void CollectAllGarbage(
       int flags = kFinalizeIncrementalMarkingMask, const char* gc_reason = NULL,
       const GCCallbackFlags gc_callback_flags = kNoGCCallbackFlags);
@@ -1526,7 +1534,7 @@
   void EnsureFillerObjectAtTop();
 
   // Ensure that we have swept all spaces in such a way that we can iterate
-  // over all objects.
+  // over all objects.  May cause a GC.
   void MakeHeapIterable();
 
   // Performs garbage collection operation.