Implement improved base::WriteFile() variants.

The new WriteFile() variants are easier to use wrappers around the
existing WriteFile() function. One variant takes a base::StringPiece,
while the other takes a base::span<const uint8_t>.

The advantages of these new functions are:
- Instead of returning the number of bytes written or -1 on failure,
  they just return bool. This makes checking the result much easier.
- Instead of taking a separate data and size pointers, they just take a
  span. This removes a container.size() call in many cases.

In addition to some basic unit tests, convert some existing WriteFile()
callers to use the new variants. Removing several existing wrappers that
are nearly identical to newly introduced variants.

Bug: 418837
Change-Id: Ie1391e9007f739da4b5752dda0dfa0989859f566
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2173693
Reviewed-by: Maxim Kolosovskiy <kolos@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Reviewed-by: Christos Froussios <cfroussios@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#765722}

• base/files/file_util.cc[diff]
• base/files/file_util.h[diff]
• base/files/file_util_unittest.cc[diff]
• chrome/browser/first_run/first_run.cc[diff]
• chrome/browser/shell_integration_linux_unittest.cc[diff]
• chrome/browser/web_applications/components/web_app_file_handler_registration_linux.cc[diff]
• chrome/browser/web_applications/components/web_app_shortcut_linux.cc[diff]
• chrome/browser/web_applications/components/web_app_shortcut_linux_unittest.cc[diff]
• components/password_manager/core/browser/export/password_manager_exporter.cc[diff]
• components/password_manager/core/browser/export/password_manager_exporter.h[diff]
• components/password_manager/core/browser/export/password_manager_exporter_unittest.cc[diff]
• content/browser/indexed_db/indexed_db_backing_store_unittest.cc[diff]
• net/proxy_resolution/proxy_config_service_linux_unittest.cc[diff]
• printing/backend/cups_helper.cc[diff]