Delegate the location change event to top-level dialog provider.

Author: crisbeto

src/lib/dialog/dialog.ts

@@ -56,7 +56,9 @@ export class MdDialog {
     // Close all of the dialogs when the user goes forwards/backwards in history or when the
     // location hash changes. Note that this usually doesn't include clicking on links (unless
     // the user is using the `HashLocationStrategy`).
-    _location.subscribe(() => this.closeAll());
+    if (!_parentDialog) {
+      _location.subscribe(() => this.closeAll());
+    }
   }
 
   /**