Fix OOM bug 3976.

src/heap/spaces.cc

Index: src/heap/spaces.cc
diff --git a/src/heap/spaces.cc b/src/heap/spaces.cc
index 827f3abb607a9ec7e8a82d58de548bd3e83c37e8..6c2b58b17e5795995911aa6a992226ce8050ef18 100644
--- a/src/heap/spaces.cc
+++ b/src/heap/spaces.cc
@@ -1019,7 +1019,8 @@ bool PagedSpace::CanExpand() {
   DCHECK(max_capacity_ % AreaSize() == 0);
   DCHECK(Capacity() <= heap()->MaxOldGenerationSize());
   DCHECK(heap()->CommittedOldGenerationMemory() <=
-         heap()->MaxOldGenerationSize());
+         heap()->MaxOldGenerationSize() +
+             PagedSpace::MaxEmergencyMemoryAllocated());
 
   // Are we going to exceed capacity for this space?
   if (!heap()->CanExpandOldGeneration(Page::kPageSize)) return false;
@@ -1046,7 +1047,8 @@ bool PagedSpace::Expand() {
 
   DCHECK(Capacity() <= heap()->MaxOldGenerationSize());
   DCHECK(heap()->CommittedOldGenerationMemory() <=
-         heap()->MaxOldGenerationSize());
+         heap()->MaxOldGenerationSize() +
+             PagedSpace::MaxEmergencyMemoryAllocated());
 
   p->InsertAfter(anchor_.prev_page());
 
@@ -1128,6 +1130,15 @@ void PagedSpace::ReleasePage(Page* page) {
 }
 
 
+intptr_t PagedSpace::MaxEmergencyMemoryAllocated() {
+  // New space and large object space.
+  static const int spaces_without_emergency_memory = 2;
+  static const int spaces_with_emergency_memory =
+      LAST_SPACE - FIRST_SPACE + 1 - spaces_without_emergency_memory;
+  return Page::kPageSize * spaces_with_emergency_memory;
+}
+
+
 void PagedSpace::CreateEmergencyMemory() {
   if (identity() == CODE_SPACE) {
     // Make the emergency block available to the allocator.