Use emergency memory in the case of out of memory during evacuation.

src/spaces.h

Index: src/spaces.h
diff --git a/src/spaces.h b/src/spaces.h
index 3fe71b2c574bb617d0155f3459f32b5999226d94..b8fa8c7eb9beb68e014b3a4d81765e2ceb69a6cf 100644
--- a/src/spaces.h
+++ b/src/spaces.h
@@ -1980,6 +1980,12 @@ class PagedSpace : public Space {
     return area_size_;
   }
 
+  void CreateEmergencyMemory();
+  void FreeEmergencyMemory();
+  void UseEmergencyMemory();
+
+  bool HasEmergencyMemory() { return emergency_memory_ != NULL; }
+
  protected:
   FreeList* free_list() { return &free_list_; }
 
@@ -2015,6 +2021,12 @@ class PagedSpace : public Space {
   // end_of_unswept_pages_ page.
   Page* end_of_unswept_pages_;
 
+  // Emergency memory is the memory of a full page for a given space, allocated
+  // conservatively before evacuating a page. If compaction fails due to out
+  // of memory error the emergency memory can be used to complete compaction.
+  // If not used, the emergency memory is released after compaction.
+  MemoryChunk* emergency_memory_;
+
   // Expands the space by allocating a fixed number of pages. Returns false if
   // it cannot allocate requested number of pages from OS, or if the hard heap
   // size limit has been hit.