Treat APKs as dangerous on Linux as well as on Android.

chrome/browser/resources/safe_browsing/download_file_types.asciipb

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # See README.md before editing this file.
 # Keep sorted by extension within logical groupings where possible.
 
 ##
 ## Top level settings
 ##
-version_id: 7
+version_id: 8
 sampled_ping_probability: 0.01
 default_file_type {
   uma_value: 18
   ping_setting: SAMPLED_PING
   platform_settings {
     danger_level: NOT_DANGEROUS
     auto_open_hint: ALLOW_AUTO_OPEN
   }
 }
 
@@ skipping 2630 matching lines @@
 }
 file_types {
   extension: "apk"
   uma_value: 20
   ping_setting: FULL_PING
   platform_settings {
     platform: PLATFORM_ANDROID
     danger_level: ALLOW_ON_USER_GESTURE
     auto_open_hint: DISALLOW_AUTO_OPEN
   }
+  platform_settings {
+    platform: PLATFORM_LINUX
+    danger_level: ALLOW_ON_USER_GESTURE
+    auto_open_hint: DISALLOW_AUTO_OPEN
+  }
 }