Make --noopt behave like an in-place precompilation.

runtime/vm/precompiler.h

Index: runtime/vm/precompiler.h
diff --git a/runtime/vm/precompiler.h b/runtime/vm/precompiler.h
index 1692edabce884427072e0892e3f18c6154c7b52a..ec9e9d0f191cccc3af852e4ee4917b94e8365ef9 100644
--- a/runtime/vm/precompiler.h
+++ b/runtime/vm/precompiler.h
@@ -79,10 +79,11 @@ class SymbolSet : public ValueObject {
 class Precompiler : public ValueObject {
  public:
   static RawError* CompileAll(
-      Dart_QualifiedFunctionName embedder_entry_points[]);
+      Dart_QualifiedFunctionName embedder_entry_points[],
+      bool reset_fields);
 
  private:
-  explicit Precompiler(Thread* thread);
+  Precompiler(Thread* thread, bool reset_fields);
 
   void DoCompileAll(Dart_QualifiedFunctionName embedder_entry_points[]);
   void ClearAllCode();
@@ -112,6 +113,8 @@ class Precompiler : public ValueObject {
   Zone* zone_;
   Isolate* isolate_;
 
+  const bool reset_fields_;
+
   bool changed_;
   intptr_t function_count_;
   intptr_t class_count_;