Populate download_file_types proto and filter it for each platform.  Except for a few extensions that were missing in the old code, these data retain the same settings as the old .cc files.

  * Move ping_settings out of platform_settings.  It'll have one value for all platforms.
  * Allow for an empty platform_settings and fill in the default_file_type's values.  This makes the config shorter.
  * Add UMA values for two missing extensions and one for when we can't load the list at all.

The data were generated by joining kDownloadFileTypes (from download_extensions.cc) and kSafeBrowsingFileTypes (from download_protection_util.cc) in a one-off conversion.  The join aimed to minimize the number of items in platform_settings by setting a default when those settings were used by the majority of platforms for that file type.

I left "ping_setting" set in all types (rather than use a default of FULL_PING) since it wouldn't be obvious in that state what the default value was.

The conversion was done with //depot/google3/experimental/users/nparker/extensions/dump_new_proto.cc


Review-Url: https://codereview.chromium.org/1929693003
Cr-Commit-Position: refs/heads/master@{#393114}
10 files changed