remove most uses of Isolate::Current in arch specific files

src/ia32/assembler-ia32-inl.h

Index: src/ia32/assembler-ia32-inl.h
diff --git a/src/ia32/assembler-ia32-inl.h b/src/ia32/assembler-ia32-inl.h
index b6ef242a2c4e5350a0d207ce9cfcdd4fa6581217..59b444a3942538be5f00550fdfba641f8e42bc78 100644
--- a/src/ia32/assembler-ia32-inl.h
+++ b/src/ia32/assembler-ia32-inl.h
@@ -329,14 +329,11 @@ Immediate::Immediate(Label* internal_offset) {
 
 
 Immediate::Immediate(Handle<Object> handle) {
-#ifdef DEBUG
-  Isolate* isolate = Isolate::Current();
-#endif
   AllowDeferredHandleDereference using_raw_address;
   // Verify all Objects referred by code are NOT in new space.
   Object* obj = *handle;
-  ASSERT(!isolate->heap()->InNewSpace(obj));
   if (obj->IsHeapObject()) {
+    ASSERT(!HeapObject::cast(obj)->GetHeap()->InNewSpace(obj));
     x_ = reinterpret_cast<intptr_t>(handle.location());
     rmode_ = RelocInfo::EMBEDDED_OBJECT;
   } else {