Add BUILD.gn for //media/ffmpeg

media/ffmpeg/BUILD.gn

+# 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.
+
+import("//media/media_options.gni")
+
+source_set("ffmpeg") {
+  assert(media_use_ffmpeg)
+  visibility = [ "//media/*" ]
+  allow_circular_includes_from = [ "//media/base" ]

[DaleCurtis, 2016/05/03 23:59:15]

I guess this is the magic? gn help says:

Danger

  In the above example, A's headers are likely to include headers from
  A's dependencies. Those dependencies may have public_configs that
  apply flags, defines, and include paths that make those headers work
  properly.

  With allow_circular_includes_from, B can include A's headers, and
  transitively from A's dependencies, without having the dependencies
  that would bring in the public_configs those headers need. The result
  may be errors or inconsistent builds.

  So when you use allow_circular_includes_from, make sure that any
  compiler settings, flags, and include directories are the same between
  both targets (consider putting such things in a shared config they can
  both reference). Make sure the dependencies are also the same (you
  might consider a group to collect such dependencies they both
  depend on).

Are we sure this is the case? I think so, but it's worth double checking.

[jrummell, 2016/05/05 00:26:12]

Done.

+  sources = [
+    "ffmpeg_common.cc",
+    "ffmpeg_common.h",
+    "ffmpeg_deleters.h",
+  ]
+  deps = [
+    "//base",
+    "//media:media_features",
+    "//media:shared_memory_support",
+    "//media/base",
+    "//third_party/ffmpeg",
+  ]
+}
+
+source_set("ffmpeg_unittests") {
+  assert(media_use_ffmpeg)
+  testonly = true
+  sources = [
+    "ffmpeg_common_unittest.cc",
+  ]
+  deps = [
+    ":ffmpeg",
+    "//base",
+    "//media",
+    "//media/base",
+    "//media/base:test_support",
+    "//testing/gtest",
+    "//third_party/ffmpeg",
+  ]
+}
+
+source_set("ffmpeg_regressiontests") {
+  assert(media_use_ffmpeg)
+  testonly = true
+  sources = [
+    "ffmpeg_regression_tests.cc",
+  ]
+  deps = [
+    ":ffmpeg",
+    "//base",
+    "//media/test:pipeline_integration_test_base",
+    "//third_party/ffmpeg",
+  ]
+}