Optimize getField by caching a closure generated from eval.

runtime/lib/mirrors.cc

Index: runtime/lib/mirrors.cc
diff --git a/runtime/lib/mirrors.cc b/runtime/lib/mirrors.cc
index 3b7391caf42238dba40a43e93faefaf52a13fafe..61d37b4bb6333d3903f08fc56fea25ce6cbeea52 100644
--- a/runtime/lib/mirrors.cc
+++ b/runtime/lib/mirrors.cc
@@ -1301,6 +1301,31 @@ DEFINE_NATIVE_ENTRY(TypeVariableMirror_upper_bound, 1) {
 }
 
 
+DEFINE_NATIVE_ENTRY(Mirrors_evalInLibraryWithPrivateKey, 2) {
+  GET_NON_NULL_NATIVE_ARGUMENT(String, expression, arguments->NativeArgAt(0));
+  GET_NATIVE_ARGUMENT(String, private_key, arguments->NativeArgAt(1));
+
+  const GrowableObjectArray& libraries =
+      GrowableObjectArray::Handle(isolate->object_store()->libraries());
+  const int num_libraries = libraries.Length();
+  Library& each_library = Library::Handle();
+  Library& ctxt_library = Library::Handle();
+  String& library_key = String::Handle();
+
+  for (int i = 0; i < num_libraries; i++) {

[Ivan Posva, 2014/02/05 22:23:44]

If the private_key is null coming in, then you will not find it anywhere in this
list.

+    each_library ^= libraries.At(i);
+    library_key = each_library.private_key();
+    if (library_key.Equals(private_key)) {
+      ctxt_library = each_library.raw();
+      break;
+    }
+  }

[Ivan Posva, 2014/02/05 22:23:44]

With the current setup I would think that you can assert that you found the
library for a given key, correct?

[rmacnak, 2014/02/05 22:56:31]

Yes, added.

+  if (ctxt_library.IsNull()) {
+    ctxt_library = Library::CoreLibrary();
+  }
+  return ctxt_library.Evaluate(expression);
+}
+
 DEFINE_NATIVE_ENTRY(TypedefMirror_declaration, 1) {
   GET_NON_NULL_NATIVE_ARGUMENT(Type, type, arguments->NativeArgAt(0));
   const Class& cls = Class::Handle(type.type_class());