proto filter: fix for Windows
proto filter: fix for Windows

Build failure:
https://ci.chromium.org/ui/p/chromium/builders/try/win10_chromium_x64_rel_ng/866079/overview

Test: manually on a standalone windows build.
Bug: 181306741
Change-Id: I47789f818b65b4459b00dde92d4a8d02d3b0ef7a

google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto