Remove guard page mechanism from promotion queue.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 1f7d8784f6b8fbf104e121212fc6e5c2b28a9196..f39ad43aa4c9a02be2036479d76c7fb3c56e8b6b 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -1365,7 +1365,6 @@ void PromotionQueue::Initialize() {
   front_ = rear_ =
       reinterpret_cast<intptr_t*>(heap_->new_space()->ToSpaceEnd());
   emergency_stack_ = NULL;
-  guard_ = false;
 }
 
 
@@ -1963,15 +1962,16 @@ class ScavengingVisitor : public StaticVisitorBase {
 
     HeapObject* target = NULL;  // Initialization to please compiler.
     if (allocation.To(&target)) {
+      // Order is important here: Set the promotion limit before storing a
+      // filler for double alignment or migrating the object. Otherwise we
+      // may end up overwriting promotion queue entries when we migrate the
+      // object.
+      heap->promotion_queue()->SetNewLimit(heap->new_space()->top());
+
       if (alignment != kObjectAlignment) {
         target = EnsureDoubleAligned(heap, target, allocation_size);
       }
 
-      // Order is important here: Set the promotion limit before migrating
-      // the object. Otherwise we may end up overwriting promotion queue
-      // entries when we migrate the object.
-      heap->promotion_queue()->SetNewLimit(heap->new_space()->top());
-
       // Order is important: slot might be inside of the target if target
       // was allocated over a dead object and slot comes from the store
       // buffer.