Add WebUI owners for things sky@ is less familar with

R=sky@chromium.org
BUG=none

Change-Id: Ia0447eae8c7bfbf6646981fd2dda592c25a95f89
Reviewed-on: https://chromium-review.googlesource.com/1098024Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Dan Beam (no longer on Chrome) <dbeam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569124}

chrome/test/base/OWNERS

 per-file js2gtest.*=dtseng@chromium.org
 per-file javascript_browser_test.*=dtseng@chromium.org
 
+per-file *javascript*=file://ui/webui/PLATFORM_OWNERS
+per-file *web_ui*=file://ui/webui/PLATFORM_OWNERS
+
 per-file *tracing*=file://base/trace_event/OWNERS
 
 per-file interactive_test_utils_mac.mm=tapted@chromium.org