Add reporting of flaky tests in browser suite (#25250)

Add reporting of flaky tests in browser suite to get orange colored
swimlane visualizations of flake, and unify reporting of flaky tests in
browser and core suites.

EMTEST_VISUALIZE=1 then shows

<img width="1540" height="874" alt="image"
src="https://github.com/user-attachments/assets/232dc021-6e84-46a0-9763-3f9e3294d28b"
/>

(in above, `flakyX` tests had 50% chance of flaking, or succeeding)

and I pattern match the "Retrying flaky test" reports in stdout log to
visualize flaked runs as orange:

<img width="1244" height="541" alt="image"
src="https://github.com/user-attachments/assets/53fe18b1-b6af-44c8-b094-8014897c030b"
/>

Author: juj

test/common.py

@@ -231,6 +231,11 @@ def decorated(self, *args, **kwargs):
   return decorated
 
 
+def record_flaky_test(test_name, attempt_count, exception_msg):
+  logging.info(f'Retrying flaky test "{test_name}" (attempt {attempt_count}/{EMTEST_RETRY_FLAKY} failed):\n{exception_msg}')
+  open(flaky_tests_log_filename, 'a').write(f'{test_name}\n')
+
+
 def flaky(note=''):
   assert not callable(note)
 
@@ -253,9 +258,7 @@ def modified(self, *args, **kwargs):
           return f(self, *args, **kwargs)
         except (AssertionError, subprocess.TimeoutExpired) as exc:
           preserved_exc = exc
-          logging.info(f'Retrying flaky test "{f.id()}" (attempt {i}/{EMTEST_RETRY_FLAKY} failed): {exc}')
-          # Mark down that this was a flaky test.
-          open(flaky_tests_log_filename, 'a').write(f'{f.__name__}\n')
+          record_flaky_test(self.id(), i, exc)
 
       raise AssertionError('Flaky test has failed too many times') from preserved_exc
 
@@ -2640,8 +2643,7 @@ def run_browser(self, html_file, expected=None, message=None, timeout=None, extr
             self.assertContained(expected, output)
           except self.failureException as e:
             if extra_tries > 0:
-              print(f'[test error in: {self.id()} (see below), automatically retrying]')
-              print(e)
+              record_flaky_test(self.id(), EMTEST_RETRY_FLAKY - extra_tries, e)
               if not self.capture_stdio:
                 print('[enabling stdio/stderr reporting]')
                 self.capture_stdio = True

test/parallel_testsuite.py

@@ -203,6 +203,8 @@ def combine_results(self, result, buffered_results):
     # shared data structures are hard in the python multi-processing world, so
     # use a file to share the flaky test information across test processes.
     flaky_tests = open(common.flaky_tests_log_filename).read().split() if os.path.isfile(common.flaky_tests_log_filename) else []
+    # Extract only the test short names
+    flaky_tests = [x.split('.')[-1] for x in flaky_tests]
 
     # The next updateResult loop will print a *lot* of lines really fast. This
     # will cause a Python exception being thrown when attempting to print to