[devtools] Temporarily disable test for landing coverage changes

The pending CL crrev.com/c/1891417 adds a new user metric, hence
this test needs to be disabled before landing+rolling. Afterwards,
the test will be re-enabled with updated expectations.

Bug: chromium:1020096
Change-Id: I409feaea758444a4f23d01386d554d46be5a0bba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1893197Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712064}

third_party/blink/web_tests/TestExpectations

@@ -5752,3 +5752,6 @@ crbug.com/963183 http/tests/devtools/network/network-cookies-pane.js [ Pass Time
 crbug.com/963183 http/tests/devtools/network/preview-searchable.js [ Pass Failure ]
 crbug.com/963183 http/tests/devtools/network/waterfall-header-height-updates.js [ Pass Failure ]
 crbug.com/963183 http/tests/devtools/network/network-search.js [ Pass Timeout Failure ]
+
+# Temporarily disabled for landing code coverage changes in DevTools
+crbug.com/1004203 http/tests/devtools/user-metrics.js [ Pass Failure ]