Disable test for upcoming DevTools change

Has to be updated for
https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2067057

TBR=jacktfranklin@chromium.org

Bug: 1050549
Change-Id: I79583541c6e1ae13311d55e1c72e762b4da3ed96
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2066780Reviewed-by: Tim van der Lippe <tvanderlippe@chromium.org>
Commit-Queue: Tim van der Lippe <tvanderlippe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743216}

third_party/blink/web_tests/TestExpectations

@@ -7543,3 +7543,6 @@ crbug.com/1053903 [ Win ] external/wpt/webxr/events_referenceSpace_reset_inline.
 crbug.com/1006759 http/tests/devtools/agents-enable-disable.js [ Skip ]
 crbug.com/1006759 http/tests/devtools/search/search-in-non-existing-resource.js [ Skip ]
 crbug.com/1006759 http/tests/devtools/sources/debugger-breakpoints/debugger-set-breakpoint-regex.js [ Skip ]
+
+# DevTools roll
+crbug.com/1050549 http/tests/devtools/unit/string-util.js [ Skip ]