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

runtime/vm/precompiler.h

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_PRECOMPILER_H_
 #define VM_PRECOMPILER_H_
 
 #include "vm/allocation.h"
 #include "vm/hash_map.h"
 #include "vm/object.h"
@@ skipping 61 matching lines @@
 
  private:
   Zone* zone_;
   DirectChainedHashMap<SymbolPair> map_;
 };
 
 
 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();
   void AddRoots(Dart_QualifiedFunctionName embedder_entry_points[]);
   void AddEntryPoints(Dart_QualifiedFunctionName entry_points[]);
   void Iterate();
   void CleanUp();
 
   void AddCalleesOf(const Function& function);
   void AddClosureCall(const ICData& call_site);
   void AddField(const Field& field);
   void AddFunction(const Function& function);
   void AddClass(const Class& cls);
   void AddSelector(const String& selector);
   bool IsSent(const String& selector);
 
   void ProcessFunction(const Function& function);
   void CheckForNewDynamicFunctions();
 
   void DropUncompiledFunctions();
 
   Thread* thread() const { return thread_; }
   Zone* zone() const { return zone_; }
   Isolate* isolate() const { return isolate_; }
 
   Thread* thread_;
   Zone* zone_;
   Isolate* isolate_;
 
+  const bool reset_fields_;
+
   bool changed_;
   intptr_t function_count_;
   intptr_t class_count_;
   intptr_t selector_count_;
   intptr_t dropped_function_count_;
 
   const GrowableObjectArray& libraries_;
   const GrowableObjectArray& pending_functions_;
   const GrowableObjectArray& collected_closures_;
   SymbolSet sent_selectors_;
   Error& error_;
 };
 
 }  // namespace dart
 
 #endif  // VM_PRECOMPILER_H_