Add a browser test for the views external protocol dialog.

chrome/test/BUILD.gn

Index: chrome/test/BUILD.gn
diff --git a/chrome/test/BUILD.gn b/chrome/test/BUILD.gn
index c0451695e6743062c8349665b47db9b7178f4b87..58e0221755c0fb6529826955229f23c9acc614c4 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -2120,7 +2120,10 @@ test("browser_tests") {
       ]
       deps += [ "//ui/views" ]
       if (!is_chromeos && (!is_mac || mac_views_browser)) {
-        sources += [ "../browser/ui/views/profiles/profile_chooser_view_browsertest.cc" ]
+        sources += [
+          "../browser/ui/views/external_protocol_dialog_browsertest.cc",
+          "../browser/ui/views/profiles/profile_chooser_view_browsertest.cc",
+        ]
       }
       if (!is_mac || mac_views_browser) {
         sources += [