Add Dart_Null, Dart_True, and Dart_False.

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
===================================================================
--- runtime/include/dart_api.h	(revision 1035)
+++ runtime/include/dart_api.h	(working copy)
@@ -139,8 +139,6 @@
  * Requires there to be a current isolate.
  */
 DART_EXPORT Dart_Handle Dart_NewPersistentHandle(Dart_Handle object);
-// TODO(turnidge): This function currently only works when passes a
-// local handle.  Make it work for both local and persistent handles.
 
 /**
  * Deallocates a persistent handle.
@@ -440,6 +438,15 @@
 // --- Objects ----
 
 /**
+ * Returns the null object.
+ *
+ * Requires there to be a current isolate.
+ *
+ * \return A handle to the null object.
+ */
+DART_EXPORT Dart_Handle Dart_Null();
+
+/**
  * Is this object null?
  */
 DART_EXPORT bool Dart_IsNull(Dart_Handle object);
@@ -567,6 +574,24 @@
 // --- Booleans ----
 
 /**
+ * Returns the True object.
+ *
+ * Requires there to be a current isolate.
+ *
+ * \return A handle to the True object.
+ */
+DART_EXPORT Dart_Handle Dart_True();
+
+/**
+ * Returns the False object.
+ *
+ * Requires there to be a current isolate.
+ *
+ * \return A handle to the False object.
+ */
+DART_EXPORT Dart_Handle Dart_False();
+
+/**
  * Is this object a Boolean?
  */
 DART_EXPORT bool Dart_IsBoolean(Dart_Handle object);