Add new Dart API function Dart_IsolateData which returns the peer isolate data associated with an i…

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
===================================================================
--- runtime/include/dart_api.h	(revision 32396)
+++ runtime/include/dart_api.h	(working copy)
@@ -876,12 +876,20 @@
 DART_EXPORT Dart_Isolate Dart_CurrentIsolate();
 
 /**
- * Returns the callback data which was passed to the isolate when it
- * was created.
+ * Returns the callback data associated with the current Isolate. This data was
+ * passed to the isolate when it was created.
  */
 DART_EXPORT void* Dart_CurrentIsolateData();
 
 /**
+ * Returns the callback data associated with the specified Isolate. This data
+ * was passed to the isolate when it was created.
+ * The embedder is responsible for ensuring the consistency of this data
+ * with respect to the lifecycle of an Isolate.
+ */
+DART_EXPORT void* Dart_IsolateData(Dart_Isolate isolate);
+
+/**
  * Returns the debugging name for the current isolate.
  *
  * This name is unique to each isolate and should only be used to make