Initial support for the desktop media pipeline on Android.

media/media_variables.gypi

Index: media/media_variables.gypi
diff --git a/media/media_variables.gypi b/media/media_variables.gypi
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+# Copyright 2015 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.
+
+# Common media variables.
+{
+  'variables': {
+    'conditions': [
+      ['OS == "android" or OS == "ios"', {
+        # Android and iOS don't use FFmpeg or libvpx by default.

[xhwang, 2015/07/15 00:14:20]

What's gonna happen when I set build_ffmpegsumo=1 on an iOS build?

[watk, 2015/07/16 20:55:14]

Your build won't work :) But even if we weren't setting this here it would break
anyway because ffmpeg wouldn't compile.

+        # Set build_ffmpegsumo=1 for Android builds to compile experimental
+        # support for FFmpeg and the desktop media pipeline.
+        # This 'variables' dict is required to ensure build_ffmpegsumo is
+        # defined when we read its value below.
+        'variables': {
+          'build_ffmpegsumo%': 0,
+        },
+        'media_use_ffmpeg%': '<(build_ffmpegsumo)',

[xhwang, 2015/07/15 00:14:20]

I found "media_use_ffmpeg" more intuitive than "build_ffmpegsumo". Can we use
media_use_ffmpeg=1 to enable this feature instead of using build_ffmpegsumo=1?

+        'media_use_libvpx%': 0,
+      }, {
+        'media_use_ffmpeg%': 1,
+        'media_use_libvpx%': 1,
+      }],
+    ],
+  },
+}