Neutralize dangerous subresource files during Save Page.

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 (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
 
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     ping. This applies to all file types where `ping_setting` is either
     `SAMPLED_PING` or `NO_PING`, and downloads where the Safe Browsing ping
     either fails, is disabled, or returns an `UNKNOWN` verdict. Exceptions are
     noted below.
 
     The warning controlled here is a generic "This file may harm your computer."
     If the Safe Browsing verdict is `UNCOMMON`, `POTENTIALLY_UNWANTED`,
     `DANGEROUS_HOST`, or `DANGEROUS`, Chrome will show that more severe warning
     regardless of this setting.
 
+    This policy also affects also how subresources are handled for *"Save As
+    ..."* downloads of complete web pages. If any subresource ends up with a
+    file type that is considered `DANGEROUS` or `ALLOW_ON_USER_GESTURE`, then
+    the filename will be changed to end in `.download`. This is done to prevent
+    the file from being opened accidentally.
+
     * `NOT_DANGEROUS`: Safe to download and open, even if the download
        was accidental. No additional warnings are necessary.
     * `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`: Potentially dangerous, but is likely harmless if
       the user is familiar with host and if the download was intentional. Chrome
       doesn't warn the user if both of the following conditions are true:
 
         * There is a user gesture associated with the network request that
@@ skipping 37 matching lines @@
     users' downloads with unknown extensions (or
     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.