WebKit: Fix PRESUBMIT_test.

The PRESUBMIT_test is broken (see https://crrev.com/c/1289164).
PRESUBMIT only filters out LayoutTests changes, but PRESUBMIT_test
passes more files and expecting all of them to be filtered out.

Bug: None
Change-Id: I3a7e03c22c0c486fc438490c4b3ea00db5cdae0f
Reviewed-on: https://chromium-review.googlesource.com/c/1289300Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600869}

third_party/WebKit/PRESUBMIT_test.py

@@ -66,13 +66,9 @@ class PresubmitTest(unittest.TestCase):
         """This verifies that CheckChangeOnUpload will skip calling
         check_blink_style.py if the affected file list is empty.
         """
-        diff_file_chromium1_h = ['some diff']
-        diff_file_chromium2_h = ['another diff']
         diff_file_layout_test_html = ['more diff']
         mock_input_api = MockInputApi()
         mock_input_api.files = [
-            MockAffectedFile('first_file_chromium.h', diff_file_chromium1_h),
-            MockAffectedFile('second_file_chromium.h', diff_file_chromium2_h),
             MockAffectedFile('LayoutTests/some_tests.html', diff_file_layout_test_html)
         ]
         # Access to a protected member _CheckStyle