Respect old space allocation limit in PagedSpace::AllocateRaw.

BUG=v8:3976
LOG=NO

Review URL: https://codereview.chromium.org/1025643002

Cr-Commit-Position: refs/heads/master@{#27364}

src/heap/heap-inl.h

@@ -698,18 +698,12 @@ void Heap::CompletelyClearInstanceofCache() {
 
 AlwaysAllocateScope::AlwaysAllocateScope(Isolate* isolate)
     : heap_(isolate->heap()), daf_(isolate) {
-  // We shouldn't hit any nested scopes, because that requires
-  // non-handle code to call handle code. The code still works but
-  // performance will degrade, so we want to catch this situation
-  // in debug mode.
-  DCHECK(heap_->always_allocate_scope_depth_ == 0);
   heap_->always_allocate_scope_depth_++;
 }
 
 
 AlwaysAllocateScope::~AlwaysAllocateScope() {
   heap_->always_allocate_scope_depth_--;
-  DCHECK(heap_->always_allocate_scope_depth_ == 0);
 }
 
 

src/heap/heap.cc

@@ -1516,6 +1516,10 @@ class ScavengeWeakObjectRetainer : public WeakObjectRetainer {
 
 void Heap::Scavenge() {
   RelocationLock relocation_lock(this);
+  // There are soft limits in the allocation code, designed to trigger a mark
+  // sweep collection by failing allocations. There is no sense in trying to
+  // trigger one during scavenge: scavenges allocation should always succeed.
+  AlwaysAllocateScope scope(isolate());
 
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap) VerifyNonPointerSpacePointers(this);

src/heap/spaces.cc

@@ -2618,7 +2618,7 @@ HeapObject* PagedSpace::SlowAllocateRaw(int size_in_bytes) {
     // If sweeper threads are active, wait for them at that point and steal
     // elements form their free-lists.
     HeapObject* object = WaitForSweeperThreadsAndRetryAllocation(size_in_bytes);
-    if (object != NULL) return object;
+    return object;
   }
 
   // Try to expand the space and allocate in the new next page.