Support weak heap references in the ConstantPool to support IsWeakObjectInOptimizedCode objects.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index 5a00d44ea2c0fa6c2e2000049f45e50aed78802c..7075a33959ac6b3b5ae555821963f7948f6ff458 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -305,12 +305,21 @@ class RelocInfo BASE_EMBEDDED {
     LAST_STANDARD_NONCOMPACT_ENUM = INTERNAL_REFERENCE
   };
 
+  enum WeakMode {
+    NOT_WEAK,
+    WEAK_IN_OPTIMIZED_CODE
+  };
 
   RelocInfo() {}
 
   RelocInfo(byte* pc, Mode rmode, intptr_t data, Code* host)
       : pc_(pc), rmode_(rmode), data_(data), host_(host) {
   }
+
+  RelocInfo(byte* pc, Mode rmode, WeakMode weak_mode, intptr_t data)
+      : pc_(pc), rmode_(rmode), data_(data), weak_mode_(weak_mode) {
+  }
+
   RelocInfo(byte* pc, double data64)
       : pc_(pc), rmode_(NONE64), data64_(data64), host_(NULL) {
   }
@@ -395,6 +404,7 @@ class RelocInfo BASE_EMBEDDED {
   }
   Code* host() const { return host_; }
   void set_host(Code* host) { host_ = host; }
+  WeakMode weak_mode() const { return weak_mode_; }
 
   // Apply a relocation by delta bytes
   INLINE(void apply(intptr_t delta));
@@ -519,7 +529,10 @@ class RelocInfo BASE_EMBEDDED {
     intptr_t data_;
     double data64_;
   };
-  Code* host_;
+  union {
+    Code* host_;
+    WeakMode weak_mode_;
+  };
   // External-reference pointers are also split across instruction-pairs
   // on some platforms, but are accessed via indirect pointers. This location
   // provides a place for that pointer to exist naturally. Its address