Implement DeclarationMirror.location for all but ParameterMirrors.

sdk/lib/mirrors/mirrors.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // For the purposes of the mirrors library, we adopt a naming
 // convention with respect to getters and setters.  Specifically, for
 // some variable or field...
 //
 //   var myField;
 //
@@ skipping 268 matching lines @@
 
   /**
    * Is this declaration top-level?
    *
    * This is defined to be equivalent to:
    *    [:mirror.owner != null && mirror.owner is LibraryMirror:]
    */
   bool get isTopLevel;
 
   /**
-   * The source location of this Dart language entity.
+   * The source location of this Dart language entity, or [:null:] if the
+   * entity is synthetic.
    *
-   * This operation is optional and may return [:null:].
+   * This operation is optional and may throw an [UnsupportedError].
    */

[gbracha, 2015/02/13 03:00:57]

So we probably should tighten the specification for this so that the location is
defined precisely. Something like (not sure if this is actually what we want):

If the reflectee is a variable, the returned location gives the position of the
variable name at its point of declaration.

If the reflectee is a library, class, typedef, function or type variable with
associated metadata, the returned location gives the position of the first
metadata declaration associated with the reflectee.

Otherwise:

If the reflectee is a library , the returned location gives the position of the
keyword 'library' at the reflectee's point of declaration.

If the reflectee is an abstract class, the returned location gives the position
of the keyword 'abstract' at the reflectee's point of declaration. Otherwise, f
the reflectee is a class, the returned location gives the position of the
keyword 'class' at the reflectee's point of declaration.

 If the reflectee is a typedef the returned location gives the position of the
of the keyword 'typedef' at the reflectee's point of declaration.

 If the reflectee is a function with a declared return type, the returned
location gives the position of the function's return type at the reflectee's
point of declaration. Otherwise. the returned location gives the position of the
function's name at the reflectee's point of declaration.

[rmacnak, 2015/02/13 20:46:34]

A library might not have a 'library foo' declaration.

Should we be specifying this in terms of the productions in the spec's grammar?

   SourceLocation get location;
 
   /**
    * A list of the metadata associated with this declaration.
    *
    * Let *D* be the declaration this mirror reflects.
    * If *D* is decorated with annotations *A1, ..., An*
    * where *n > 0*, then for each annotation *Ai* associated
    * with *D, 1 <= i <= n*, let *ci* be the constant object
    * specified by *Ai*. Then this method returns a list whose
@@ skipping 923 matching lines @@
    *
    * When used as metadata on an import of "dart:mirrors", this metadata does
    * not apply to the library in which the annotation is used, but instead
    * applies to the other libraries (all libraries if "*" is used).
    */
   final override;
 
   const MirrorsUsed(
       {this.symbols, this.targets, this.metaTargets, this.override});
 }