Omit unused code metadata from precompiled snapshots.

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 ec8dfffa4e1cf3abfd110606b8eb138ee8f79051..25dc6124321b566ccbc1841bc59d475c89d3b57c 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -1049,9 +1049,12 @@ class RawCode : public RawObject {
   RawObject* owner_;  // Function, Null, or a Class.
   RawExceptionHandlers* exception_handlers_;
   RawPcDescriptors* pc_descriptors_;
+  RawArray* stackmaps_;
+  RawObject** to_snapshot() {
+    return reinterpret_cast<RawObject**>(&ptr()->stackmaps_);
+  }
   RawArray* deopt_info_array_;
   RawArray* static_calls_target_table_;  // (code-offset, function, code).
-  RawArray* stackmaps_;
   RawLocalVarDescriptors* var_descriptors_;
   RawArray* inlined_metadata_;
   RawArray* comments_;