Add download_file_types.proto with ascii->binary conversion, as a resource.

chrome/browser/resources/safe_browsing/README.md

Index: chrome/browser/resources/safe_browsing/README.md
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+# Behavior of Download File Types in Chrome
+
+This describes how to adjust file-type download behavior in
+Chrome including interactions with Safe Browsing.  The metadata described
+here, and stored in `download_file_types.asciipb`, will be both baked into
+Chrome released and pushable to Chrome between releases. http://crbug.com/596555
+
+Rendered version of this file: https://chromium.googlesource.com/chromium/src/+/master/chrome/browser/resources/safe_browsing/README.md
+
+
+## Procedure for adding a new type
+  * Edit `download_file_types.asciipb`. Update `histograms.xml`
+  * Get it reviewed, submit.
+  * Push via component update (PROCEDURE TBD)
+
+## Guidelines for a DownloadFileType entry:
+See `download_file_types.proto` for all fields.
+
+  * `extension`: Value must be unique within the config. It should be
+    lowercase ASCII and not contain a dot.  If there _is_ a duplicate,
+    first one wins.  Only the `default_file_type` should leave this unset.
+
+  * `uma_value`: Value must be unique and match one in the
+    `SBClientDownloadExtensions` enum in `histograms.xml`.
+
+  * `is_archive`: `True` if this filetype is a container for other files.
+     Leave it unset for `false`.
+
+  * `platform_settings`: (repeated) Must have one entry with an unset
+     `platform` field, and optionally additional entries with overrides
+     for one or more platforms.  An unset `platform` field acts as a
+     default for any platforms that don't have an override.  There should
+     not be two settings with the same `platform`, but if there are,
+     first one wins.  Keep them sorted by platform.
+
+  * `platform_settings.danger_level`: (required)
+    * `NOT_DANGEROUS`: Safe to download and open, even if the download
+       was accidental.
+    * `DANGEROUS`: Always warn the user that this file may harm their
+      computer.  We let them continue or discard the file.  If Safe
+      Browsing returns a SAFE verdict, we still warn the user.
+    * `ALLOW_ON_USER_GESTURE`: Warn the user normally but skip the warning
+      if there was a user gesture or the user visited this site before
+      midnight last night (i.e. is a repeat visit).  If Safe Browsing
+      returns a SAFE verdict for this file, it won't show a warning.
+
+  * `platform_settings.auto_open_hint`: Required.
+    * `ALLOW_AUTO_OPEN`: File type can be opened automatically if the user
+      selected that option from the download tray on a previous download
+      of this type.
+    * `DISALLOW_AUTO_OPEN`:  Never let the file automatically open.
+      Files that should be disallowed from auto-opening include those that
+      execute arbitrary or harmful code with user privileges, or change
+      configuration of the system to cause harmful behavior immediately
+      or at some time in the future. We *do* allow auto-open for files
+      that upon opening sufficiently warn the user about the fact that it
+      was downloaded from the internet and can do damage.  **Note**:
+      Some file types (e.g.: .local and .manifest) aren't dangerous
+      to open.  However, their presence on the file system may cause
+      potentially dangerous changes in behavior for other programs. We
+      allow automatically opening these file types, but always warn when
+      they are downloaded.
+
+  * `platform_settings.ping_setting`:  Required.  This controls what sort
+     of ping is sent to Safe Browsing and if a verdict is checked before
+     the user can access the file.
+    * `SAMPLED_PING`: Don't send a full Safe Browsing ping, but
+       send a no-PII "light-ping" for a random sample of SBER users.
+       This should be the default for unknown types.  The verdict won't
+       be used.
+    * `NO_PING`:  Don’t send any pings.  This file is whitelisted. All
+      NOT_DANGEROUS files should normally use this.
+    * `FULL_PING`: Send full pings and use the verdict. All dangerous
+      file should use this.
+
+  * TODO(nparker): Support this: `platform_settings.unpacker`:
+     optional. Specifies which archive unpacker internal to Chrome
+     should be used.  If potentially dangerous file types are found,
+     Chrome will send a full-ping for the entire file.  Otherwise, it'll
+     follow the ping settings. Can be one of UNPACKER_ZIP or UNPACKER_DMG.
+
+## Guidelines for the top level DownloadFileTypeConfig entry:
+  * `version_id`: Must be increased (+1) every time the file is checked in.
+     Will be logged to UMA.
+
+  * `sampled_ping_probability`: For what fraction of extended-reporting
+    users' downloads with unknown extensions (or
+    ping_setting=SAMPLED_PING) should we send light-pings? [0.0 .. 1.0]
+
+  * `file_type`: The big list of all known file types. Keep them
+     sorted by extension.
+
+  * `default_file_type`: Settings used if a downloaded file is not in
+    the above list.  `extension` is ignored, but other settings are used.
+    The ping_setting should be SAMPLED_PING for all platforms.
+