Script to push download_file_types.pb to all platforms, via Component Updater

chrome/browser/resources/safe_browsing/README.md

 # 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
+Chrome released and pushable to Chrome between releases (via
+`FileTypePolicies` class).  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`, edit `download_stats.cc` (necessary
-    until it gets replaced), and update `histograms.xml`
-  * Get it reviewed, submit.
-  * Push via component update (PROCEDURE TBD)
+## Procedure for adding/modifying file type(s)
+  * **Edit** `download_file_types.asciipb` and update `histograms.xml`
+  * Get it reviewed, **submit.**
+  * **Push** it to all users via component update:
+    * Wait 1-3 day for this to run on Canary to verify it doesn't crash Chrome.
+    * In a synced checkout, generate protos for all platforms:
+        * % `ninja -C out-gn/Debug
+         chrome/browser/resources/safe_browsing:make_all_file_types_protobuf`
+    * That will instruct you to run another command to push the files to GCS.
+      You must a member of chrome-file-type-policies-pushers@google.com to have
+      access to the GCS bucket.
+    * The Component Updater system will notice those files and push them to
+      users withing ~6 hours. If not, contact `waffles@.`
+
 
 ## Guidelines for a DownloadFileType entry:
 See `download_file_types.proto` for all fields.
 
   * `extension`: (required) 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`: (required) must be unique and match one in the
     `SBClientDownloadExtensions` enum in `histograms.xml`.
@@ skipping 70 matching lines @@
     ping_setting=SAMPLED_PING) should we send light-pings? [0.0 .. 1.0]
 
   * `file_types`: 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. Only the
     first platform_setting is used.