[headless] Disable headless protocol browsertests.

Various of the tests in the suite have been individually disabled due
to flakiness, but according to flake-portal most if not all of the tests
in the suite are flaky, so disable them all.

The individually disabled tests should be reviewed when re-enable this
suite, since at least some look to be instances of the same general
issue with tests flakily timing-out.

TBR=pfeldman

Bug: 1107396
Change-Id: Ie6540e92999503c2c83bd132f447860b4c2c8b45
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2307216Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Auto-Submit: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789934}

headless/BUILD.gn

@@ -617,7 +617,10 @@ test("headless_browsertests") {
     "test/headless_browser_test.cc",
     "test/headless_browser_test.h",
     "test/headless_client_browsertest.cc",
-    "test/headless_protocol_browsertest.cc",
+
+    # TODO(https://crbug.com/1107396): These tests flakily timeout.
+    #"test/headless_protocol_browsertest.cc",
+
     "test/headless_test_launcher.cc",
     "test/test_network_interceptor.cc",
     "test/test_network_interceptor.h",