feat: add app.getApplicationNameForProtocol API (#20399)

* Add GetApplicationNameForProtocol.

* Fix Windows implementation.

* Fix up test.

* Add documentation.

* Implement for real on Linux using xdg-mime.

Also ensure we allow blocking calls here to avoid errant DCHECKing.

* Improve docs for Linux.

* Clean up tests.

* Add a note about not relying on the precise format.

* Update docs/api/app.md

Co-Authored-By: Shelley Vohr <codebytere@github.com>

* Remove needless `done()`s from tests.

* Use vector list initialization.

* Add a simple test for isDefaultProtocolClient.

* Remove unneeded include and skip a test on Linux CI.

* We no longer differentiate between CI and non-CI test runs.

shell/browser/browser.h

@@ -92,6 +92,8 @@ class Browser : public WindowListObserver {
   bool IsDefaultProtocolClient(const std::string& protocol,
                                gin_helper::Arguments* args);
 
+  base::string16 GetApplicationNameForProtocol(const GURL& url);
+
   // Set/Get the badge count.
   bool SetBadgeCount(int count);
   int GetBadgeCount();