Add Dart_IdentityHash to the embedding API.

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 070d646c975b60b8603d4836301f084ec22aca7d..3fd21df97db5f576021cb6e5c7e6954baffaa6f6 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -599,6 +599,50 @@ DART_EXPORT bool Dart_IdentityEquals(Dart_Handle obj1, Dart_Handle obj2) {
 }
 
 
+DART_EXPORT uint64_t Dart_IdentityHash(Dart_Handle obj) {
+  Isolate* isolate = Isolate::Current();
+  DARTSCOPE(isolate);
+
+  const Object& object = Object::Handle(isolate, Api::UnwrapHandle(obj));
+  if (!object.IsInstance() && !object.IsNull()) {
+    return 0;
+  }

[siva, 2014/05/02 17:29:59]

Maybe use the pattern:
  const Instance& obj = Api::UnwrapInstanceHandle(isolate, exception);
  if (obj.IsNull()) {
    RETURN_TYPE_ERROR(isolate, exception, Instance);
  }

+
+  const Library& libcore = Library::Handle(isolate, Library::CoreLibrary());
+  const String& function_name = String::Handle(isolate,
+                                               String::New("identityHashCode"));
+  const Function& function =
+      Function::Handle(isolate,
+                       libcore.LookupFunctionAllowPrivate(function_name));
+  if (function.IsNull()) {
+    UNREACHABLE();
+    return 0;
+  }
+
+  const Array& arguments = Array::Handle(isolate, Array::New(1));
+  arguments.SetAt(0, object);
+  const Object& result =
+      Object::Handle(isolate, DartEntry::InvokeFunction(function, arguments));
+
+  if (result.IsSmi()) {
+    return Smi::Cast(result).Value();
+  }
+  if (result.IsMint()) {
+    const Mint& mint = Mint::Cast(result);
+    if (!mint.IsNegative()) {
+      return mint.AsInt64Value();
+    }
+  }
+  if (result.IsBigint()) {
+    const Bigint& bigint = Bigint::Cast(result);
+    if (BigintOperations::FitsIntoUint64(bigint)) {
+      return BigintOperations::ToUint64(bigint);
+    }
+  }

[siva, 2014/05/02 17:29:59]

We have a similar pattern in Dart_NativeIntegerArgument maybe you could factor
this part out into a static function.

[rmacnak, 2014/05/02 21:19:13]

Given the lack of failure cases here I don't think there's a good refactoring.
But Dart_NativeIntegerArgument and Dart_IntegerToInt64 could share some code if
we're okay with slightly less specific error messages.

+  return 0;
+}
+
+
 DART_EXPORT Dart_Handle Dart_HandleFromPersistent(
     Dart_PersistentHandle object) {
   Isolate* isolate = Isolate::Current();