Add Isolate.current getter, returning the current isolate as an Isolate object.

sdk/lib/isolate/isolate.dart

Index: sdk/lib/isolate/isolate.dart
diff --git a/sdk/lib/isolate/isolate.dart b/sdk/lib/isolate/isolate.dart
index 6a2bfb43eace7e641ca6fc260a9a653f37f8ff8d..35d2a8b15c90cb444672753f7b197714faa39ab3 100644
--- a/sdk/lib/isolate/isolate.dart
+++ b/sdk/lib/isolate/isolate.dart
@@ -120,6 +120,15 @@ class Isolate {
                              this.terminateCapability});
 
   /**
+   * Return the current [Isolate].
+   *
+   * The isolate gives access to the capabilities needed to inspect,
+   * pause or kill the isolate, and allows granting these capabilities
+   * to others.
+   */
+  external static Isolate get current;
+
+  /**
    * Creates and spawns an isolate that shares the same code as the current
    * isolate.
    *