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 ebd93aeff9dd9da41e11b55e14ad319471552cb3..91a84b0fb7b85915ad6f541a332869e3ad9b6765 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -1094,6 +1094,7 @@ 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; }
@@ -3518,6 +3519,8 @@ 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_;