Add map-based read barrier to WeakCell

src/ia32/macro-assembler-ia32.h

Index: src/ia32/macro-assembler-ia32.h
diff --git a/src/ia32/macro-assembler-ia32.h b/src/ia32/macro-assembler-ia32.h
index e62c7d8b4d23d6013b0cddda89db67be31c96773..adbcdc0409b88841daf27363ebd78522189769f8 100644
--- a/src/ia32/macro-assembler-ia32.h
+++ b/src/ia32/macro-assembler-ia32.h
@@ -298,11 +298,22 @@ class MacroAssembler: public Assembler {
   // Compare the given value and the value of weak cell.
   void CmpWeakValue(Register value, Handle<WeakCell> cell, Register scratch);
 
-  void GetWeakValue(Register value, Handle<WeakCell> cell);
+  void GetWeakValue(Register value, Register scratch, Handle<WeakCell> cell);
+
+  // Gets the given value without triggering the read barrier (you must
+  // immediately discard the value returned). You might want to use
+  // CmpWeakValue instead.
+  void GetWeakValueNoReadBarrier(Register value, Handle<WeakCell> cell);
+
+  // Load the value of the weak cell in the value register. Branch to the given
+  // miss label if the weak cell was cleared.
+  void LoadWeakValue(Register value, Handle<WeakCell> cell, Register scratch,
+                     Label* miss);
 
   // Load the value of the weak cell in the value register. Branch to the given
   // miss label if the weak cell was cleared.
-  void LoadWeakValue(Register value, Handle<WeakCell> cell, Label* miss);
+  void LoadWeakValueNoReadBarrier(Register value, Handle<WeakCell> cell,
+                                  Label* miss);
 
   // ---------------------------------------------------------------------------
   // JavaScript invokes