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

chrome/common/safe_browsing/download_file_types.proto

+// 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.
+//
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+
+package safe_browsing;
+
+// Next id: 5
+message DownloadFileType {
+  // The file extension, without a dot.
+  // This must be unique within one DownloadFileTypeConfig
+  optional string extension = 1;  // required
+
+  // Must be unique and not reused, and be consistent with
+  // SBClientDownloadExtensions enum in histograms.xml
+  optional int64 uma_value = 2;  // required
+
+  // True if is an archive type.
+  optional bool is_archive = 3;  // required
+
+
+  enum DownloadDangerLevel {

[asanka, 2016/04/06 02:12:30]

Nit: The /Download/ prefixes aren't strictly necessary since it's implicit that
all defined properties apply to DownloadFileType.

[Nathan Parker, 2016/04/11 20:12:07]

Good call, done.

+    // Safe. Or at least not known to be dangerous. Safe to
+    // download and open, even if the download was accidental.
+    NOT_DANGEROUS = 0;
+
+    // Require confirmation before downloading. An additional user
+    // gesture may not be required if the download was from a
+    // familiar site and the download was initiated via a user
+    // action.
+    ALLOW_ON_USER_GESTURE = 1;
+
+    // Always require confirmation when downloading.
+    DANGEROUS = 2;
+  }
+
+  enum DownloadAutoOpenHint {
+    // File type can be opened automatically.
+    ALLOW_AUTO_OPEN = 1;
+
+    // The file type should not be allowed to open automatically.
+    //
+    // Criteria for disallowing a file type from opening automatically:
+    //
+    // Includes file types that upon opening may either:
+    //   * ... execute arbitrary or harmful code with user privileges.
+    //   * ... change configuration of the system to cause harmful behavior
+    //     immediately or at some time in the future.
+    //
+    // Doesn't include file types that upon opening:
+    //   * ... sufficiently warn the user about the fact that:
+    //     - This file was downloaded from the Internet.
+    //     - Opening it can make specified changes to the system.
+    //     (Note that any such warnings need to be displayed prior to
+    //      the harmful logic being executed).
+    //   * ... does nothing particularly dangerous, despite the act
+    //     of downloading itself being dangerous (E.g. .local and
+    //     .manifest files).
+    DISALLOW_AUTO_OPEN = 2;
+  }
+
+  enum PlatformType {
+    ALL = 0;

[asanka, 2016/04/06 02:12:31]

This is exposed as DownloadFileType::ALL? Perhaps PLATFORM_ALL or ALL_PLATFORMS
would be clearer?

[Nathan Parker, 2016/04/11 20:12:07]

I renamed it to PLATFORM_ANY since that's actually more accurate, and made it
the default so most entries can leave it out.  We'll also leave out is_archive
and use the default.  These two shorten the .asciipb file a bit and make it
easier to read.

+    PLATFORM_ANDROID = 1;
+    PLATFORM_CHROME_OS = 2;
+    PLATFORM_LINUX = 3;
+    PLATFORM_MAC = 4;
+    PLATFORM_WINDOWS = 5;
+  }
+
+  enum PingSetting {
+    // Don’t send pings except maybe light-pings.
+    TREAT_AS_UNKNOWN = 0;
+    // Don’t send any pings.
+    NO_PING = 1;
+    // Send full pings and use the verdicts.
+    SEND_FULL_PING = 2;
+    // Send full pings and but ignore the SAFE verdict.
+    SEND_FULL_PING_IGNORE_SAFE = 3;
+  }
+
+  // Next id: 5
+  message PlatformSettings {
+    optional PlatformType platform = 1;
+    optional DownloadDangerLevel danger_level = 2;  // required
+    optional DownloadAutoOpenHint auto_open_hint = 3;  // required
+    optional PingSetting ping_setting = 4;  // required
+  };
+
+  // In the canonical list, this must have at least one entry and it can
+  // have platform=ALL to act as the default for any OS not listed.  In
+  // the files served via gstatic, each _<OS>.pb file will have only its
+  // own single entry, with |platform| not populated.

[asanka, 2016/04/06 02:12:31]

As far as maintainability goes, would it be easier to have the _<OS>.asciipb in
the Chromium tree as well? That way each platform only needs to ship their
relevant settings instead of all settings. It might be a bit more involved to
maintain, but we'd need to keep the _<OS>.asciipb in sync with the Chromium tree
anyway.

Or/also, we can assume a <PLATFORM_ALL, NOT_DANGEROUS, ALLOW_AUTO_OPEN,
TREAT_AS_UNKNOWN> entry always exists if none of the platform entries match the
current platform.

[Nathan Parker, 2016/04/11 20:12:07]

My plan was to have one asciipb file, but then we could generate per-platform
binary files (will do in a separate CL).  That way it's easy to compare
platforms and there'll be no divergence on the cross-platform settings
(extension name, uma, etc). Is there a usecase for varying settings other than
those in platform_settings? 
That's an interesting idea. It could fall back to the default_file_type's
setting. Once I generate the full list in proto form, I'll look at how common
that one is to see if it's worthwhile.

[asanka, 2016/04/11 20:45:02]

SGTM. I had misunderstood what we were going to store server-side vs in the
Chromium tree.

+  repeated PlatformSettings platform_settings = 4; // required >= 1
+};
+
+
+// The file_types.asciipb config file is composed of one of these messages.
+// Next id: 5
+message DownloadFileTypeConfig {
+  // Monotonically increasing version number.  Will be logged to UMA.
+  optional uint32 version_id = 1;
+
+  // For what fraction of extended-reporting users’ downloads
+  // with unknown extensions should we send light-pings?
+  // [0..1]
+  optional float light_ping_probability = 2;
+
+  // List of all known types.
+  repeated DownloadFileType file_type = 3;

[asanka, 2016/04/06 02:12:31]

Nit: style guide says this should be called "file_types"

[Nathan Parker, 2016/04/11 20:12:07]

Done.

+
+  // Settings used if a file is not in the above list.  “Extension” is ignored.
+  optional DownloadFileType default_file_type = 4;
+}
+