[turbofan] Use FastCloneShallow[Array|Object]Stub if possible.

src/ast.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_AST_H_
 #define V8_AST_H_
 
 #include "src/v8.h"
 
 #include "src/assembler.h"
@@ skipping 1489 matching lines @@
 
   // Mark all computed expressions that are bound to a key that
   // is shadowed by a later occurrence of the same key. For the
   // marked expressions, no store code is emitted.
   void CalculateEmitStore(Zone* zone);
 
   // Assemble bitfield of flags for the CreateObjectLiteral helper.
   int ComputeFlags(bool disable_mementos = false) const {
     int flags = fast_elements() ? kFastElements : kNoFlags;
     flags |= has_function() ? kHasFunction : kNoFlags;
+    if (depth() == 1 && !has_elements() && !may_store_doubles()) {
+      flags |= kShallowProperties;
+    }
     if (disable_mementos) {
       flags |= kDisableMementos;
     }
     return flags;
   }
 
   enum Flags {
     kNoFlags = 0,
     kFastElements = 1,
     kHasFunction = 1 << 1,
-    kDisableMementos = 1 << 2
+    kShallowProperties = 1 << 2,
+    kDisableMementos = 1 << 3
   };
 
   struct Accessors: public ZoneObject {
     Accessors() : getter(NULL), setter(NULL) {}
     Expression* getter;
     Expression* setter;
   };
 
   BailoutId CreateLiteralId() const { return BailoutId(local_id(0)); }
 
@@ skipping 2051 matching lines @@
 
  private:
   Zone* zone_;
   AstValueFactory* ast_value_factory_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_AST_H_