[tricium] Add string_view to list of C++ headers

Recipe-Nontrivial-Roll: build
Change-Id: I76c2db161677852b005f2b934ff96f7369844fb4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1900486
Commit-Queue: Jasper Chapman-Black <jaspercb@chromium.org>
Reviewed-by: Quinten Yearsley <qyearsley@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>

cpplint.py

@@ -368,6 +368,7 @@ _CPP_HEADERS = frozenset([
     'stdexcept',
     'streambuf',
     'string',
+    'string_view',
     'strstream',
     'system_error',
     'thread',