Implement DeclarationMirror.location for all but ParameterMirrors.

sdk/lib/mirrors/mirrors.dart

Index: sdk/lib/mirrors/mirrors.dart
diff --git a/sdk/lib/mirrors/mirrors.dart b/sdk/lib/mirrors/mirrors.dart
index d16e62eecb7fc4e63e4518e7ffd4398b8c562fda..a52bc8802df41beef26cbbe2ef48327bdcf52979 100644
--- a/sdk/lib/mirrors/mirrors.dart
+++ b/sdk/lib/mirrors/mirrors.dart
@@ -286,9 +286,10 @@ abstract class DeclarationMirror implements Mirror {
   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;