Disentangle assembler from isolate.

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index bb59b5e7dce4a0c45d9b2606565d9f1631852675..e1a2a57a32575ed0b359f057ba8cc7f94d0f9f5e 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -2699,8 +2699,6 @@ bool Isolate::Init(Deserializer* des) {
 #endif
 #endif
 
-  code_aging_helper_ = new CodeAgingHelper(this);
-
   { // NOLINT
     // Ensure that the thread has a valid stack guard.  The v8::Locker object
     // will ensure this too, but we don't have to use lockers if we are only
@@ -2716,6 +2714,8 @@ bool Isolate::Init(Deserializer* des) {
     return false;
   }
 
+  code_aging_helper_ = new CodeAgingHelper(this);
+
 // Initialize the interface descriptors ahead of time.
 #define INTERFACE_DESCRIPTOR(V) \
   { V##Descriptor(this); }