fuchsia: suppress -Wconversion warnings
fuchsia: suppress -Wconversion warnings

Bug: fuchsia:56258
Bug: fuchsia:58162
Change-Id: I6b631888d83ef9bec6abdb7fedc0c9156e815d71
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/mini_chromium/+/2405542
Reviewed-by: Mark Mentovai <f1b5a91d4d6ad523f2610114591c007e75d15084@chromium.org>

chromium/mini_chromium,chromium/mini_chromium,chromium/mini_chromium