[fuchsia] Use the Ozone scenic platform to run WebEngine browser-tests.

Bug: 865172
Change-Id: I687021367afc08315226049d18302b70856aa595
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2366743
Auto-Submit: Wez <wez@chromium.org>
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#802417}

fuchsia/engine/test/web_engine_test_launcher.cc

@@ -50,7 +50,7 @@ class WebEngineTestLauncherDelegate : public content::TestLauncherDelegate {
 int main(int argc, char** argv) {
   base::CommandLine::Init(argc, argv);
   auto* command_line = base::CommandLine::ForCurrentProcess();
-  command_line->AppendSwitchASCII(switches::kOzonePlatform, "headless");
+  command_line->AppendSwitchASCII(switches::kOzonePlatform, "scenic");
   command_line->AppendSwitchASCII(switches::kEnableLogging, "stderr");
   command_line->AppendSwitch(switches::kDisableGpu);