Fix multi-isolate build:

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 bafb1750277de5462c2281f38342196d9ca42fa3..946022adb402716e3568b2e13569bf72b3610778 100644
--- a/src/ia32/macro-assembler-ia32.h
+++ b/src/ia32/macro-assembler-ia32.h
@@ -56,7 +56,11 @@ class PostCallGenerator;
 // MacroAssembler implements a collection of frequently used macros.
 class MacroAssembler: public Assembler {
  public:
-  MacroAssembler(void* buffer, int size);
+  // The isolate parameter can be NULL if the macro assembler should
+  // not use isolate-dependent functionality. In this case, it's the
+  // responsibility of the caller to never invoke such function on the
+  // macro assembler.
+  MacroAssembler(Isolate* isolate, void* buffer, int size);
 
   // ---------------------------------------------------------------------------
   // GC Support
@@ -580,7 +584,10 @@ class MacroAssembler: public Assembler {
 
   void Move(Register target, Handle<Object> value);
 
-  Handle<Object> CodeObject() { return code_object_; }
+  Handle<Object> CodeObject() {
+    ASSERT(!code_object_.is_null());
+    return code_object_;
+  }
 
 
   // ---------------------------------------------------------------------------