Precompilation: drop unused types and type arguments and empty classes and libraries.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 8fffdb4d3396e6c0cec6ee97746e264aec1d0317..ee8782a77904b9e49635aac6898addd997a8ef17 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -1090,6 +1090,7 @@ class Class : public Object {
     return raw_ptr()->direct_subclasses_;
   }
   void AddDirectSubclass(const Class& subclass) const;
+  void ClearDirectSubclasses() const;
 
   // Check if this class represents the class of null.
   bool IsNullClass() const { return id() == kNullCid; }
@@ -3514,6 +3515,8 @@ class Library : public Object {
   RawLibrary* ImportLibraryAt(intptr_t index) const;
   bool ImportsCorelib() const;
 
+  void DropDependencies() const;
+
   // Resolving native methods for script loaded in the library.
   Dart_NativeEntryResolver native_entry_resolver() const {
     return raw_ptr()->native_entry_resolver_;