Restore back pointer from Instructions to Code

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index 1fdb20c02d1e36897a9f060e774c5aedb157e024..55d9dc0ef8860891fc32350475f0d92e5144c000 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -1087,6 +1087,14 @@ class RawObjectPool : public RawObject {
 class RawInstructions : public RawObject {
   RAW_HEAP_OBJECT_IMPLEMENTATION(Instructions);
 
+  RawObject** from() {
+    return reinterpret_cast<RawObject**>(&ptr()->code_);

[rmacnak, 2015/09/29 16:50:12]

Need to exclude code_ when running precompiled or the heap verifier will be
unhappy.

[Cutch, 2015/09/29 23:24:29]

This is handled inside RawInstructions::VisitInstructionsPointers in
raw_object.cc

+  }
+  RawCode* code_;
+  RawObject** to() {
+    return reinterpret_cast<RawObject**>(&ptr()->code_);
+  }
+
   int32_t size_;
 
   // Variable length data follows here.