Refine spec for TypedefMirror.value and for ClosureMirror.findInContext.

sdk/lib/mirrors/mirrors.dart

Index: sdk/lib/mirrors/mirrors.dart
===================================================================
--- sdk/lib/mirrors/mirrors.dart	(revision 30385)
+++ sdk/lib/mirrors/mirrors.dart	(working copy)
@@ -875,6 +875,10 @@
 abstract class TypedefMirror implements TypeMirror {
   /**
    * The defining type for this typedef.
+   * If the the type referred to by the reflectee is a function type 
+   * *F*, the result will be [:FunctionTypeMirror:] reflecting *F*
+   * which is abstract and has an abstract method [:call:] whose 
+   * signature corresponds to *F*.
    *
    * For instance [:void f(int):] is the referent for [:typedef void f(int):].
    */