Capture FAILURES!!! when running Android scenario_app tests.

testing/scenario_app/bin/android_integration_tests.dart

@@ -170,15 +170,20 @@ void main(List<String> args) async {
     });
 
     await step('Running instrumented tests...', () async {
-      final int exitCode = await pm.runAndForward(<String>[
+      final (int exitCode, StringBuffer out) = await pm.runAndCapture(<String>[
         adb.path,
         'shell',
         'am',
         'instrument',
-        '-w', 'dev.flutter.scenarios.test/dev.flutter.TestRunner',
+        '-w',
+        'dev.flutter.scenarios.test/dev.flutter.TestRunner',
       ]);
       if (exitCode != 0) {
-        panic(<String>['could not install test apk']);
+        panic(<String>['instrumented tests failed to run']);
+      }
+      if (out.toString().contains('FAILURES!!!')) {
+        stdout.write(out);
+        panic(<String>['1 or more tests failed']);
       }
     });
   } finally {

testing/scenario_app/bin/utils/process_manager_extension.dart

@@ -45,4 +45,11 @@ extension RunAndForward on ProcessManager {
   Future<int> runAndForward(List<String> cmd) async {
     return pipeProcessStreams(await start(cmd), out: stdout);
   }
+
+  /// Runs [cmd], and captures the stdout and stderr pipes.
+  Future<(int, StringBuffer)> runAndCapture(List<String> cmd) async {
+    final StringBuffer buffer = StringBuffer();
+    final int exitCode = await pipeProcessStreams(await start(cmd), out: buffer);
+    return (exitCode, buffer);
+  }
 }