Add GN targets for third_party/libwebm

R=brettw@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/266893002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@271056 0039d316-1c4b-4281-b951-d872f2087c98

BUILD.gn

@@ -45,6 +45,7 @@ group("root") {
     "//third_party/leveldatabase",
     "//third_party/libpng",
     "//third_party/libusb",
+    "//third_party/libwebm",
     "//third_party/libwebp",
     "//third_party/ots",
     "//third_party/qcms",

third_party/libwebm/BUILD.gn

+# Copyright 2014 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.
+
+source_set("libwebm") {
+  sources = [
+    "source/mkvmuxer.cpp",
+    "source/mkvmuxerutil.cpp",
+    "source/mkvwriter.cpp",
+  ]
+
+  # mkvmuxerutil.cpp redefines the _CRT_RAND_S macro. This is the only thing
+  # that blocks this target from using Chromium compiler settings.
+  configs -= [ "//build/config/compiler:chromium_code" ]
+  configs += [ "//build/config/compiler:no_chromium_code" ]
+}