Add Dart_IdentityHash to the embedding API.

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
diff --git a/runtime/include/dart_api.h b/runtime/include/dart_api.h
index 5648eb60ab981addcdf3003878016d14d400ca1e..5495659af057a70109e8df26d4bb5eb2ea9a4a4c 100755
--- a/runtime/include/dart_api.h
+++ b/runtime/include/dart_api.h
@@ -391,6 +391,13 @@ DART_EXPORT Dart_Handle Dart_ToString(Dart_Handle object);
 DART_EXPORT bool Dart_IdentityEquals(Dart_Handle obj1, Dart_Handle obj2);
 
 /**
+ * Returns a hash code for the argument. The hash code of objects that are equal
+ * according to Dart_IdentityEquals will return the same hash code, but the hash
+ * codes of non-equal objects are not necessarily distinct.

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

The comment should also document the input param and the return values

(see comment above for Dart_IdentityEquals)

Maybe the signature should be

DART_EXPORT Dart_Handle Dart_IdentityHash(Dart_Handle obj, uint64_t* value);

That way you can return error in case of input problems.

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

Done.
There is no error case. Dart_IdentityEquals accepts any handle so
Dart_IdentityHash must as well. We merely give low-quality hashes for
non-instances.

+ */
+DART_EXPORT uint64_t Dart_IdentityHash(Dart_Handle obj);
+
+/**
  * Allocates a handle in the current scope from a persistent handle.
  */
 DART_EXPORT Dart_Handle Dart_HandleFromPersistent(Dart_PersistentHandle object);