Adding V8 api to get memory statistics of spaces in V8::Heap.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index b90a8da5d9a76a6799fedb43cb55ffff06fdeb3b..b65d993f02ba23b03e35375a9a8b27d125acd1e5 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -661,6 +661,9 @@ class Heap {
     return NULL;
   }
 
+  // Returns name of the space.
+  const char* GetSpaceName(int idx);
+
   bool always_allocate() { return always_allocate_scope_depth_ != 0; }
   Address always_allocate_scope_depth_address() {
     return reinterpret_cast<Address>(&always_allocate_scope_depth_);