Add third_party/wuffs

Skia (https://skia.googlesource.com/skia) is a 2-D graphics library,
already in use by Chromium as third_party/skia. Wuffs
(https://github.com/google/wuffs) is a memory-safe programming language
whose standard library includes a GIF image decoder. Wuffs' standard
library is also available as transpiled C code. From Skia's (and
Chromium's) point of view, Wuffs' standard library is just another C
library. It's just not hand-written C.

Upstream Skia is moving to use Wuffs for GIF image decoding
(https://bugs.chromium.org/p/skia/issues/detail?id=8235). For Chromium,
this commit (adding third_party/wuffs, but no change in the generated
binaries yet) is the first in a series of commits (see
crbug.com/1014044) to have Skia-in-Chromium also use Wuffs.

Wuffs is released under the Apache License 2.0:
https://github.com/google/wuffs/blob/master/LICENSE

Bug: 1014044
Change-Id: I6b41794af09b07aacc48d519651bc397e761ad71
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1859536Reviewed-by: Chris Palmer <palmer@chromium.org>
Reviewed-by: Matthew Denton <mpdenton@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nigel Tao <nigeltao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708485}

DEPS

@@ -323,6 +323,10 @@ vars = {
   # the commit queue can handle CLs rolling libexpat
   # and whatever else without interference from each other.
   'libexpat_revision': '25d3c190c69ea7f98e2826f901fd9e28b6f7f3fd',
+  # Three lines of non-changing comments so that
+  # the commit queue can handle CLs rolling wuffs
+  # and whatever else without interference from each other.
+  'wuffs_revision': '4080840928c0b05a80cda0d14ac2e2615f679f1a',
 
   # TODO(crbug.com/941824): The values below need to be kept in sync
   # between //DEPS and //buildtools/DEPS, so if you're updating one,
@@ -1507,6 +1511,11 @@ deps = {
   'src/third_party/webrtc':
     Var('webrtc_git') + '/src.git' + '@' + '8e13e6ed3dfbd2009f4c2e781dc19621d9dd8ca3',
 
+  # Wuffs' canonical repository is at github.com/google/wuffs, but we use
+  # Skia's mirror of Wuffs, the same as in upstream Skia's DEPS file.
+  'src/third_party/wuffs/src':
+    Var('skia_git') + '/external/github.com/google/wuffs.git' + '@' +  Var('wuffs_revision'),
+
   'src/third_party/xdg-utils': {
       'url': Var('chromium_git') + '/chromium/deps/xdg-utils.git' + '@' + 'd80274d5869b17b8c9067a1022e4416ee7ed5e0d',
       'condition': 'checkout_linux',

third_party/.gitignore

@@ -243,6 +243,7 @@
 /win_toolchain/.timestamps
 /win_toolchain/files
 /wix
+/wuffs/src
 /xdg-utils
 /xstream/lib/
 /xulrunner-sdk

third_party/wuffs/BUILD.gn

+# Copyright 2019 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.
+
+static_library("wuffs") {
+  defines = [
+    # Copy/pasting from "src/release/c/wuffs-*.c":
+    #
+    # ----
+    #
+    # Wuffs ships as a "single file C library" or "header file library" as per
+    # https://github.com/nothings/stb/blob/master/docs/stb_howto.txt
+    #
+    # To use that single file as a "foo.c"-like implementation, instead of a
+    # "foo.h"-like header, #define WUFFS_IMPLEMENTATION before #include'ing or
+    # compiling it.
+    #
+    # ----
+    "WUFFS_IMPLEMENTATION",
+
+    # Continuing to copy/paste:
+    #
+    # ----
+    #
+    # Defining the WUFFS_CONFIG__MODULE* macros are optional, but it lets users
+    # of Wuffs' .c file whitelist which parts of Wuffs to build. That file
+    # contains the entire Wuffs standard library, implementing a variety of
+    # codecs and file formats. Without this macro definition, an optimizing
+    # compiler or linker may very well discard Wuffs code for unused codecs,
+    # but listing the Wuffs modules we use makes that process explicit.
+    # Preprocessing means that such code simply isn't compiled.
+    #
+    # ----
+    #
+    # For Chromium, we're only interested in particular image codes (e.g. GIF)
+    # and their dependencies (e.g. BASE, LZW).
+    "WUFFS_CONFIG__MODULES",
+    "WUFFS_CONFIG__MODULE__BASE",
+    "WUFFS_CONFIG__MODULE__GIF",
+    "WUFFS_CONFIG__MODULE__LZW",
+  ]
+
+  sources = [
+    "src/release/c/wuffs-v0.2.c",
+  ]
+}

third_party/wuffs/OWNERS

+nigeltao@chromium.org
+scroggo@chromium.org
+# COMPONENT: Internals>Skia

third_party/wuffs/README.chromium

+Name: Wuffs (Wrangling Untrusted File Formats Safely)
+Short name: Wuffs
+URL: https://github.com/google/wuffs
+Version: 0.2.0-rc.1
+Revision: 4080840928c0b05a80cda0d14ac2e2615f679f1a
+Security critical: yes
+License: Apache 2.0
+
+Description:
+Codecs (compression, images, etc.) written in a custom memory-safe programming
+language, transpiled to C.
+
+Local Modifications:
+None.