[infra] Use safaridriver to launch Safari

For some reason, we launched Safari from a file, which since macOS 10.14
requires the user to confirm the operation in a modal dialog which
caused timeouts.

* Removed unused http test driver port option.
* Added some basic tests for test.py's browser interactions.

Bug: b/208186791
Change-Id: I070529148d37bf312f219c576abca3da972f73e6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/204202
Commit-Queue: Alexander Thomas <[email protected]>
Reviewed-by: William Hesse <[email protected]>

Author: athomas

pkg/test_runner/bin/launch_browser.dart

@@ -35,7 +35,6 @@ void main(List<String> arguments) {
   var configuration = TestConfiguration(
       configuration: Configuration(
           "dummy-configuration", null, null, null, runtime, null));
-  var executable = configuration.browserLocation;
-  var browser = Browser.byRuntime(runtime, executable);
+  var browser = Browser.fromConfiguration(configuration);
   browser.start(arguments[1]);
 }