Only reload libraries when they may have been modified.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 6c95eb1ad0c9bc7db9b9f16786cd7ee5c3f47f6c..79c0f4b852607ee7b29fffd0c53e347979fbc413 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -3385,6 +3385,9 @@ class TokenStream : public Object {
 class Script : public Object {
  public:
   RawString* url() const { return raw_ptr()->url_; }
+
+  // The actual url which was loaded from disk, if provided by the embedder.
+  RawString* resolved_url() const { return raw_ptr()->resolved_url_; }
   bool HasSource() const;
   RawString* Source() const;
   RawString* GenerateSource() const;  // Generates source code from Tokenstream.
@@ -3440,8 +3443,14 @@ class Script : public Object {
                         const String& source,
                         RawScript::Kind kind);
 
+  static RawScript* New(const String& url,
+                        const String& resolved_url,
+                        const String& source,
+                        RawScript::Kind kind);
+
  private:
   void set_url(const String& value) const;
+  void set_resolved_url(const String& value) const;
   void set_source(const String& value) const;
   void set_kind(RawScript::Kind value) const;
   void set_load_timestamp(int64_t value) const;