WPT Waterfall timeouts debugging.

Still getting timeouts when setting `--test-types` to omit wdspec tests
(also note that this flag is buggy so setting it twice overwrites the
values, so we were only running reftests on the previous try).

Try disabling multi-processing this time.

Bug: 1023835
Change-Id: I2131a31ba3ba796cb7a82536a6b0bd3c44862a90
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1919324
Auto-Submit: Luke Z <lpz@chromium.org>
Commit-Queue: Robert Ma <robertma@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#716042}

testing/scripts/run_wpt_tests.py

@@ -52,9 +52,6 @@ class WPTTestAdapter(common.BaseIsolatedScriptArgsAdapter):
             "--binary-arg=--enable-blink-features=MojoJS,MojoJSTest",
             "--webdriver-binary=../../out/Release/chromedriver",
             "--headless",
-            # TODO(lpz): Consider removing --processes and compute automatically
-            # from multiprocessing.cpu_count()
-            "--processes=5",
             "--no-capture-stdio",
             "--no-manifest-download",
             "--no-pause-after-test",
@@ -75,8 +72,10 @@ class WPTTestAdapter(common.BaseIsolatedScriptArgsAdapter):
             # (crbug.com/1023835) The flags below are temporary to aid debugging
             "--log-mach=-",
             "--log-mach-verbose",
-            "--test-type=testharness",
-            "--test-type=reftest"
+            # See if multi-processing affects timeouts.
+            # TODO(lpz): Consider removing --processes and compute automatically
+            # from multiprocessing.cpu_count()
+            #"--processes=5",
         ])
         return rest_args