Disconnects code objects from infrequently used unoptimized functions.

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 28803)
+++ runtime/vm/object.h	(working copy)
@@ -1477,6 +1477,9 @@
   // Sets function's code and code's function.
   void SetCode(const Code& value) const;
 
+  // Detaches code from the function by setting the code to null.
+  void DetachCode() const;
+
   // Disables optimized code and switches to unoptimized code.
   void SwitchToUnoptimizedCode() const;
 
@@ -1487,6 +1490,9 @@
   RawCode* unoptimized_code() const { return raw_ptr()->unoptimized_code_; }
   void set_unoptimized_code(const Code& value) const;
   static intptr_t code_offset() { return OFFSET_OF(RawFunction, code_); }
+  static intptr_t unoptimized_code_offset() {
+    return OFFSET_OF(RawFunction, unoptimized_code_);
+  }
   inline bool HasCode() const;
 
   // Returns true if there is at least one debugger breakpoint
@@ -2661,6 +2667,9 @@
  public:
   intptr_t size() const { return raw_ptr()->size_; }  // Excludes HeaderSize().
   RawCode* code() const { return raw_ptr()->code_; }
+  static intptr_t code_offset() {
+    return OFFSET_OF(RawInstructions, code_);
+  }
   RawArray* object_pool() const { return raw_ptr()->object_pool_; }
   static intptr_t object_pool_offset() {
     return OFFSET_OF(RawInstructions, object_pool_);